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The XVIth Banff Meeting for Allograft Pathology was held in Banff, Alberta, Canada, from September 19 to 23, 2022, as a joint meeting with the Canadian Society of Transplantation. In addition to a key focus on the impact of microvascular inflammation and biopsy-based transcript analysis on the Banff Classification, further sessions were devoted to other aspects of kidney transplant pathology, in particular T cell-mediated rejection, activity and chronicity indices, digital pathology, xenotransplantation, clinical trials, and surrogate endpoints. Although the output of these sessions has not led to any changes in the classification, the key role of Banff Working Groups in phrasing unanswered questions, and coordinating and disseminating results of investigations addressing these unanswered questions was emphasized. This paper summarizes the key Banff Meeting 2022 sessions not covered in the Banff Kidney Meeting 2022 Report paper and also provides an update on other Banff Working Group activities relevant to kidney allografts., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

The Thrombotic Microangiopathy Banff Working Group (TMA-BWG) was formed in 2015 to survey current practices and develop minimum diagnostic criteria (MDC) for renal transplant TMA (Tx-TMA). To generate consensus among pathologists and nephrologists, the TMA BWG designed a 3-Phase study. Phase I of the study is presented here. Using the Delphi methodology, 23 panelists with >3 years of diagnostic experience with Tx-TMA pathology listed their MDC suggesting light, immunofluorescence, and electron microscopy lesions, clinical and laboratory information, and differential diagnoses. Nine rounds (R) of consensus resulted in MDC validated during two Rs using online evaluation of whole slide digital images of 37 biopsies (28 TMA, 9 non-TMA). Starting with 338 criteria the process resulted in 24 criteria and 8 differential diagnoses including 18 pathologic, 2 clinical, and 4 laboratory criteria. Results show that 3/4 of the panelists agreed on the diagnosis of 3/4 of cases. The process also allowed definition refinement for 4 light and 4 electron microscopy lesions. For the first time in Banff classification, the Delphi methodology was used to generate consensus. The study shows that Delphi is a democratic and cost-effective method allowing rapid consensus generation among numerous physicians dealing with large number of criteria in transplantation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Afrouzian, Kozakowski, Liapis, Broecker, Truong, Avila-Casado, Regele, Seshan, Ambruzs, Farris, Buob, Chander, Cheraghvandi, Clahsen-van Groningen, de Almeida Araujo, Ertoy Baydar, Formby, Galesic Ljubanovic, Herrera Hernandez, Honsova, Mohamed, Ozluk, Rabant, Royal, Stevenson, Toniolo and Taheri.)

The Banff community summoned the TMA Banff Working Group to develop minimum diagnostic criteria (MDC) and recommendations for renal transplant TMA (Tx-TMA) diagnosis, which currently lacks standardized criteria. Using the Delphi method for consensus generation, 23 nephropathologists (panelists) with >3 years of diagnostic experience with Tx-TMA were asked to list light, immunofluorescence, and electron microscopic, clinical and laboratory criteria and differential diagnoses for Tx-TMA. Delphi was modified to include 2 validations rounds with histological evaluation of whole slide images of 37 transplant biopsies (28 TMA and 9 non-TMA). Starting with 338 criteria in R1, MDC were narrowed down to 24 in R8 generating 18 pathological, 2 clinical, 4 laboratory criteria, and 8 differential diagnoses. The panelists reached a good level of agreement (70%) on 76% of the validated cases. For the first time in Banff classification, Delphi was used to reach consensus on MDC for Tx-TMA. Phase I of the study (pathology phase) will be used as a model for Phase II (nephrology phase) for consensus regarding clinical and laboratory criteria. Eventually in Phase III (consensus of the consensus groups) and the final MDC for Tx-TMA will be reported to the transplantation community., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Afrouzian, Kozakowski, Liapis, Broecker, Truong, Avila-Casado, Regele, Seshan, Ambruzs, Farris, Buob, Chander, Cheraghvandi, Clahsen-van Groningen, de Almeida Araujo, Ertoy Baydar, Formby, Galesic Ljubanovic, Herrera Hernandez, Honsova, Mohamed, Ozluk, Rabant, Royal, Stevenson, Toniolo and Taheri.)

The XV. Banff conference for allograft pathology was held in conjunction with the annual meeting of the American Society for Histocompatibility and Immunogenetics in Pittsburgh, PA (USA) and focused on refining recent updates to the classification, advances from the Banff working groups, and standardization of molecular diagnostics. This report on kidney transplant pathology details clarifications and refinements to the criteria for chronic active (CA) T cell-mediated rejection (TCMR), borderline, and antibody-mediated rejection (ABMR). The main focus of kidney sessions was on how to address biopsies meeting criteria for CA TCMR plus borderline or acute TCMR. Recent studies on the clinical impact of borderline infiltrates were also presented to clarify whether the threshold for interstitial inflammation in diagnosis of borderline should be i0 or i1. Sessions on ABMR focused on biopsies showing microvascular inflammation in the absence of C4d staining or detectable donor-specific antibodies; the potential value of molecular diagnostics in such cases and recommendations for use of the latter in the setting of solid organ transplantation are presented in the accompanying meeting report. Finally, several speakers discussed the capabilities of artificial intelligence and the potential for use of machine learning algorithms in diagnosis and personalized therapeutics in solid organ transplantation., (© 2020 The Authors. American Journal of Transplantation published by Wiley Periodicals LLC on behalf of The American Society of Transplantation and the American Society of Transplant Surgeons.)

The XIII Banff meeting, held in conjunction the Canadian Society of Transplantation in Vancouver, Canada, reviewed the clinical impact of updates of C4d-negative antibody-mediated rejection (ABMR) from the 2013 meeting, reports from active Banff Working Groups, the relationships of donor-specific antibody tests (anti-HLA and non-HLA) with transplant histopathology, and questions of molecular transplant diagnostics. The use of transcriptome gene sets, their resultant diagnostic classifiers, or common key genes to supplement the diagnosis and classification of rejection requires further consensus agreement and validation in biopsies. Newly introduced concepts include the i-IFTA score, comprising inflammation within areas of fibrosis and atrophy and acceptance of transplant arteriolopathy within the descriptions of chronic active T cell-mediated rejection (TCMR) or chronic ABMR. The pattern of mixed TCMR and ABMR was increasingly recognized. This report also includes improved definitions of TCMR and ABMR in pancreas transplants with specification of vascular lesions and prospects for defining a vascularized composite allograft rejection classification. The goal of the Banff process is ongoing integration of advances in histologic, serologic, and molecular diagnostic techniques to produce a consensus-based reporting system that offers precise composite scores, accurate routine diagnostics, and applicability to next-generation clinical trials., (© 2016 The Authors. American Journal of Transplantation published by Wiley Periodicals, Inc. on behalf of American Society of Transplant Surgeons.)

The Banff working group on preimplantation biopsy was established to develop consensus criteria (best practice guidelines) for the interpretation of preimplantation kidney biopsies. Digitally scanned slides were used (i) to evaluate interobserver variability of histopathologic findings, comparing frozen sections with formalin-fixed, paraffin-embedded tissue of wedge and needle core biopsies, and (ii) to correlate consensus histopathologic findings with graft outcome in a cohort of biopsies from international medical centers. Intraclass correlations (ICCs) and univariable and multivariable statistical analyses were performed. Good to fair reproducibility was observed in semiquantitative scores for percentage of glomerulosclerosis, arterial intimal fibrosis and interstitial fibrosis on frozen wedge biopsies. Evaluation of frozen wedge and core biopsies was comparable for number of glomeruli, but needle biopsies showed worse ICCs for glomerulosclerosis, interstitial fibrosis and tubular atrophy. A consensus evaluation form is provided to help standardize the reporting of histopathologic lesions in donor biopsies. It should be recognized that histologic parameters may not correlate with graft outcome in studies based on organs deemed to be acceptable after careful clinical assessment. Significant limitations remain in the assessment of implantation biopsies., (© Copyright 2016 The American Society of Transplantation and the American Society of Transplant Surgeons.)

Diffuse peritubular capillary C4d deposition in renal allograft biopsies is associated with donor-specific antibodies (DSA) and graft failure. The significance of focal C4d+ is unclear. We reviewed 368 biopsies from 301 patients performed for renal dysfunction or proteinuria over 5 years. Diffuse C4d+, focal C4d+ and C4d- detected by immunofluorescence occurred in 9.5%, 20.9% and 69.4% of biopsies, respectively. Patients were similar in gender, age, cause of renal disease, donor source, HLA mismatch, serum creatinine at baseline and interval from transplantation to biopsy. Diffuse and focal C4d+ were associated with acute cellular rejection (p < 0.001). Transplant glomerulopathy was associated with diffuse C4d+. DSA at the time of biopsy, were positive in 79.3% of diffusely C4d+ patients, 68.8% of those with focal C4d+ (p = 0.27) and 9.9% of patients with C4d- (p < 0.001, compared to either the focal or diffuse groups, respectively). Allograft survival at 40 months was lower in diffuse C4d+ compared to the C4d- group (p = 0.014), but not when compared to the focal C4d+ group. There was a clear trend toward worse graft survival in patients with focal C4d+ in this time interval, but focal C4d+ compared to both diffuse C4d+ and C4d-groups was not statistically significant (p = 0.08).

This study assessed the incidence of cytomegalovirus (CMV) disease and associated outcomes after oral ganciclovir prophylaxis in renal transplantation. A retrospective analysis was performed of all adult renal transplant recipients at a single transplant center transplanted between August 16, 1996, and December 31, 2000. CMV disease prophylaxis included ganciclovir 1000 mg orally thrice daily prescribed for 90 d in D-/R+ cases and 180 d in D+/R- and D+/R+ cases. Forty (9.1%) of 470 patients studied were diagnosed with CMV disease, which varied significantly by CMV serostatus and number of HLA-DR matches. The highest incidence of disease, 26.2%, was in D+/R- patients with zero HLA-DR matches. Five-year graft survival was 56.8% with CMV disease compared with 79.1% without (P < 0.001). Five-year graft survival with CMV disease was 75.9% with one or two HLA-DR matches versus 16.2% with zero HLA-DR matches (P < 0.001). CMV remains an important factor in long-term graft survival after oral ganciclovir prophylaxis. However, we have observed that the adverse impact of CMV disease on graft survival is apparent only in patients with zero HLA-DR matches. These results call for the development of new CMV disease prophylaxis and treatment strategies in patients with zero HLA-DR matches. In addition, organ allocation policies discouraging combining CMV-seropositive donors and zero HLA-DR matches may be worth consideration.

Background: Quantitative blood polymerase chain reaction (PCR) for cytomegalovirus (CMV) is used to direct therapy in kidney transplant patients, but cytomegalic inclusions are rarely found in allograft renal biopsies even with an elevated serum creatinine and apparent CMV disease. The relationship between quantitative blood CMV and renal allograft pathology is unknown., Methods: Thirteen biopsy samples were available for analysis from patients suspected of CMV disease, who had a buffy coat CMV-PCR drawn within 2-5 days of a renal allograft biopsy for an elevated creatinine. All were evaluated for CMV pathologically, by light microscopy, immunohistochemistry, in situ hybridization and tissue PCR., Results: Qualitative and quantitative buffy coat CMV-PCR were positive in 10/13 (77%) patients. Tissue CMV-PCR was positive in five (50%) biopsies, including two with CMV inclusions and three with no inclusions. Quantitative buffy coat CMV-PCR levels did not correlate with detection of CMV inclusions in renal tissue. Paradoxically, quantitative buffy coat CMV-PCR was low (239 and 538 copies/microg of DNA) when CMV inclusions were detected. All five biopsies with acute rejection were associated with CMV viraemia and two of the five with allograft CMV inclusions. A quantitative buffy coat CMV-PCR of <100 copies/microg of DNA ruled out disease with CMV inclusions., Conclusions: CMV nephropathy is much more common than previously reported when sensitive techniques are used for detection in tissue. Acute rejection and CMV viraemia occur commonly together in patients at risk for CMV. Quantitative buffy coat CMV-PCR does not correlate with the presence of CMV inclusions. These findings have implications for management of patients who have elevated serum creatinine and are at risk for CMV disease.

To determine whether transplanted metanephroi grow, differentiate, and function in hosts that differ in major histocompatibility complex loci (RT1 loci in rats) from donors in a defined way, we implanted metanephroi from embryonic day (E) 15 PVG (RT1(c)) rat embryos into the omentum of nonimmunosupressed uninephrectomized PVG-RT1(avl) (host) rats. By 4 wk posttransplantation, metanephroi had grown and differentiated such that glomeruli, proximal and distal tubules, and collecting ducts had normal structure and ultrastructure. At 12 wk posttransplantation, weights of metanephroi were 54 +/- 8 mg. Inulin clearances were 0.9 +/- 0.3 microl. min(-1). 100 g rat wt(-1). In vitro, splenocytes from PVG rats stimulated the proliferation of cells originating from both PVG-RT1(avl) rats in which a transplant had been performed and PVG-RT1(avl) rats with no transplant. Full-thickness PVG-RT1(avl) skin engrafted normally on PVG-RT1(avl) rats in which PVG metanephroi had been previously implanted and metanephroi retained a normal appearance. In contrast, skin from PVG rats sloughed, and the tubular architecture of metanephroi was obliterated by a mononuclear cell infiltrate consistent with acute rejection. Here we show for the first time that functional chimeric kidneys develop from metanephroi transplanted across the MHC into nonimmunosupressed hosts and provide evidence that a state of peripheral immune tolerance secondary to T cell "ignorance" permits their survival.