王政祿（天津市第一中心醫(yī)院病理科，天津 300192）

The Banff 2015 Kidney Meeting Report：Current Challenges in Rejection Classification and Prospects for Adopting Molecular Pathology

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.

Abbreviations： aah， hyaline arteriolar thickening；ah， arteriorlar hyalinosis； ABMR， antibody-mediated rejection ； ASHI， American Society for Histocompatibility and Immunogenetics； BWG， Banff Working Groups；cg， glomerular double contours； ci， interstitial fibrosis；ct， tubular atrophy ； cv， vascular fibrous intimal thickening； DGF， delayed graft function ； DSA，donor-specific antibody； DSAST， donor-specific antibody-specific transcript； ELISA， enzyme-linked immunosorbent assay； EM，electron microscopy；FDA， U.S. Food and Drug Administration ； FFPE，for-malin-fixed， paraffin-embedded； g， glomerulitis；GBM， glomerular basement membrane； HS， highly sensitized ； i， inflammation ； IFTA， interstitial fibrosis and tubular atrophy； i-IFTA， interstitial inflammation in areas of interstitial fibrosis and tubular atrophy； IHC， immunohistochemistry； IVIG，intravenous immunoglobulin ； mRNA， messenger RNA ； miRNA， microRNA ； MPGN， membranoproliferative glomeru-lonephritis； MVI， microvascular invasion； PAS， periodic acid-Schiff； PCR， polymerase chain reaction ； ptc， peritubular capillaritis； PTC，peritubular capillary ； t， tubulitis； TCMR， T cellmediated rejection ； TG， transplant glomerulopathy；ti， total inflammation； TMA， thrombotic microangiopathy；v，intimal arteritis； VCA， vascularized composite allograft.

Introduction

The ⅩⅢ Banff meeting was held October 5～10， 2015，in Vancouver， Canada， in conjunction with the annual meeting of the Canadian Society of Transplantation. A total of 451 delegates from 28 countries attended the conference， including pathologists， immunologists，physicians， surgeons， and immunogeneticists. The main aims of the 2015 conference were to review the clinical impact of the 2013 changes related to the new diagnostic criteria for antibody-mediated rejection （ABMR）1and to identify the next set of challenges in transplant diagnostics. Given the limitations of the current Banff system， a need for a more integrated diagnostic system，including complementary approaches as a companion to the current morphologic gold standard， are needed.Consequently， the prospects for introducing molecular diagnostics into the Banff classification were a main focus. Accordingly， the Banff 2015 conference was preceded by a full-day premeeting on “Precision Diagnostics” in transplantation. This included presentations from key opinion leaders of the American Society for Histocompatibility and Immunogenetics （ASHI）with the aim to foster collaboration between the societies in transplant diagnostics. This meeting report summarizes the main outcomes from the Banff kidney，pancreas， and vascularized com-posite allograft（VCA） sessions； the main conclusions from the 2015 Banff liver， heart， and lung sessions will be published elsewhere. The XIV Banff meeting will be held jointly with the Catalan Society of Transplantation in Barcelona， Spain， March 27 ～ 31， 2017.

Results From the Banff Working Groups and New Developments

Banff Working Groups （BWGs） have been formed at each of the last four Banff conferences to address and potentially modify specific aspects of the classification2.Their activities are dynamic and goal directed；therefore， the Banff community decided during the 2015 conference to close or suspend working groups whose work has been completed and published， in press， and/ or incorporated into the classification（isolated endarteritis， Banff Initiative for Quality Assurance in Transplantation， fibrosis， implantation biopsy， polyoma virus， C4d-negative ABMR， and glomerular lesions BWGs）1，3-7. The BWG on highly sensitized patients presented the results of three surveys of pathologists， clinicians， and histocompatibility laboratory directors， comprising 193 centers from six continents， and revealed wide heterogeneity among participating centers regarding immune modulation/desensitization practices， timing of kidney allograft protocol biopsies， and testing and reporting of HLA antibody and donor-specific antibody （DSA） levels.The TCMR working group's main aims and related ongoing studies are detailed in Table 1 and are expected to provide novel insights by the next Banff meeting.

Four new BWGs have been formed： （i） thrombotic microangiopathy， （ii） recurrent glomerular diseases，（iii） diagnostic electron microscopy， and （iv）composite surrogate end points. The aim of the latter BWG is to build and validate a composite scoring system integrating histopathology with other relevant allograft biomarkers to predict long-term allograft outcome as a potential end point for next-generation clinical trials in the area. The currently active and new working groups and their aims， leaders， initial findings（if appropriate）， and ongoing work are listed in Table 1.As an outlook on future challenges， the Banff process founder Kim Solez gave a keynote address on tissue engineering pathology， a new pathology discipline that will likely play an increasing role in future Banff meetings， as transplant pathologists need to embrace tissue engineering pathology in the era of regenerative medicine8.

New Challenges in Rejection Diagnosis and Classification

During the 2015 Banff conference， there was lively discussion about diagnostic concerns regarding ABMR， T cell-mediated rejection （TCMR）， and mixed rejection in renal allografts. Important new data were presented revealing the heterogeneity of clinical expression of ABMR with consequent difficulties for diagnosis. In addition， important insights were presented by ASHI members on how testing for DSAs and interpretation of results should be included in the Banff classification （Table 2）.

Table 1 Summary of active Banff 2015 working groups

Table 2 Key points addressed by the American Society for Histocompatibility and Immunogenetics expert panel during the Banff 2015 conference for improving the current diagnostic system

Recent evidence indicates that subclinical ABMR has important clinical implications， even in non-highly sensi- tized patients with de novo DSAs9. As noted by Orandi et al， “Increasing numbers of transplant physicians are encountering this problem， which may become more common given new therapeutic agents and new organ allocation policies”10.

A growing number of centers perform high-risk renal transplants， thereby intensifying the need for improved assessment of subclinical ABMR11and the clinical implications of its kinetics and response to therapy10.Advances in antibody testing by multiplex bead array assays have greatly enhanced the sensitivity and precision of detection of circulating DSAs12.Accumulating evidence supports the concept that not all DSAs are equivalent and that DSA properties（ability to bind complement or IgG subclass）， beyond simple positivity and mean fluorescence intensity，are associated with distinct outcomes and injury phenotypes in preexisting or recurrent as well as de novo DSAs13-20. These distinct DSA properties and their relationship with distinct allograft injury patterns is also increasingly demonstrated in other solid organ transplants such as liver21and heart22. It was also noted that time course， kinetics， and properties of DSA fluctuate15，23. Consequently， interpretation of studies evaluating sera at a single time point， especially late after transplantation， should be interpreted with caution because of potential selection bias24-25. Despite the usefulness of multiplex bead array assays， inherent limitations， technical issues， and lack of available DSA data at the time of biopsy make diagnoses complex.It was reemphasized that non-anti-HLA DSAs can produce allograft injury alone or together with anti-HLA DSAs26-28. These observations raise the question of whether ABMR can be diagnosed in the absence of documented DSAs based on ABMR-related pathology only， namely， microcirculation inflammation， C4d deposition， and vasculitis with or without increased expression of DSA-associated gene sets29-30.

Furthermore， many cases of ABMR in renal allografts，particularly late ABMR associated with de novo DSAs，can present as mixed ABMR and TCMR31. Renal allograft biopsies with microvascular inflammation plus intimal arteritis also frequently show tubulointerstitial TCMR changes9，32. These cases likely represent mixed ABMR and TCMR and， not surprisingly， are often not responsive to treatment for either ABMR or TCMR alone32-33. This may be related in large part to the fact that many cases of late ABMR are associated with nonadherence34. TCMR is also a documented predisposing factor for the future development of de novo DSAs， as demonstrated in two recent studies9，11.More data are needed regarding transplant glomerulopathy （TG） or double contours with or without microcirculation inflammation in terms of disease activity and progression and thus necessity of treatment.A key question discussed during the meeting was whether patients with TG should be treated for active ABMR or whether it should be accepted that these patients will progress to graft loss regardless of treatment. A study by Kahwaji et al35showed in a small cohort of patients， all with TG， that those with active microvascular invasion （MVI） were significantly more likely to show stabilization of graft function with intravenous immunoglobulin （IVIG） and rituximab than patients with similar histology who were not treated， whereas patients with TG without active MVI did not benefit from treatment with IVIG and rituximab.The findings suggest that the decision as to whether to treat patients with TG， particularly those with DSAs，should depend on whether there is concurrent active MVI. More recently， a pilot randomized control trial showed that patients with chronic ABMR that responded to complement blockade eculizumab by improved GFR were the ones that had complement （C1q binding）circulating anti-HLA DSAs at the time of diagnosis36.This important issue will be addressed further at Banff 2017.

DSA Against HLA or Other Antigens in the Diagnosis of ABMR

The Banff 2013 classification requires the presence of “serologic evidence of DSA against HLA or other antigens” （criterion 3） for diagnosis of both acute/active and chronic active ABMR； however， peritubular capillary C4d deposition is highly specific for DSA and potentially identifies antibodies against endothelial antigens and DSA currently not tested for in many laboratories （e.g. antibodies to HLA DP， non-HLA antigens）. Furthermore， a recent study showed similar graft outcomes， at least in chronic active ABMR， in cases with C4d or DSA and those with C4d and DSA37.The attendees of kidney-specific sessions at Banff 2015 were polled as to whether the requirement for DSA for diagnosis of ABMR can be waived in biopsies showing both morphologic evidence of acute or chronic tissue injury （as defined in criterion 1 of the Banff 2013 classification for acute/active and chronic active ABMR， respectively） and C4d staining in peritubular capillaries； however， the opinion of the majority of the Banff panel （with some dissenters） was that this was not warranted by the current data. It was instead decided to add the following phrase to the classification for both acute/active and chronic active ABMR， as a corollary to criterion 3： “Biopsies meeting the above histologic criteria and showing diffuse or focal linear peritubular capillary C4d staining on frozen or paraffin sections are associated with a high probability of ABMR and should［undergo］ prompt expedited DSA testing.” Table 3 summarizes this new addition to the classification， and the complete and most updated Banff classifications for renal allograft diagnoses are shown in Table 3.

A set of transcripts （DSA-specific transcripts ［DSASTs］）was determined to be differentially expressed in renal allograft biopsies from DSA-positive versus-negative patients29， a finding that was later confirmed independently at a different center30. Consequently，DSASTs have the potential to identify cases of ABMR in patients with non-detectable HLA DSA. It is not clear to what extent， if any， transcript patterns will be affected by prognostically different DSAs，including anti-HLA class Ⅰ versusclass Ⅱ ； antibodies with high versus low mean fluorescence intensity；complement-binding versus non-complement-binding antibodies15-17，19； and antibodies of different IgG subclasses24. Further prospective validation is required.

Chronic Active TCMR and Interstitial Inflammation in Areas of Interstitial Fibrosis and Tubular Atrophy

Table 3 Updated 2015 Banff classification categories

Continued table 3

The most recent Banff criteria for chronic active TCMR 38 list only vascular lesions （arterial intimal fibrosis with mononuclear cell infiltration within the sclerotic intima；transplant arteriopathy， Table 3）. This is likely neither complete nor fully accurate ； however，sufficient data are currently not available to properly define this diagnosis. Interstitial inflammation in areas of interstitial fibrosis and tubular atrophy （i-IFTA）was discussed among participants of the Banff meeting as a potential lesion of chronic active TCMR. Although the association of i-IFTA with decreased graft survival is well documented39-41， the pathogenesis of i-IFTA and to what extent this represents a manifestation of TCMR is much less clear. Similarly， the significance of tubulitis in atrophic tubules is unclear. Gene expression studies on microdissected foci of i-IFTA might help assess this. In light of the established deleterious effect on graft survival of i-IFTA and IFTA with Banff inflammation （i） score＞0， it was agreed that i-IFTA should be included as part of the Banff lesion scoring. Moreover， i-IFTA should be graded as mild，moderate， or severe based on whether it involves 10%-25%，26%-50%， or ＞ 50%， respectively， of the scarred cortical tissue （Table 4， and supplementary material for scoring criteria）. Note that the extent of i-IFTA is not analogous to the Banff total inflammation score， the latter representing the sum of inflammation in scarred and non-scarred areas of the cortex.Consequently， it was decided to modify the Banff 2007 criteria by adding a statement （Table 3， category 4），reflecting findings that lesions of transplant arteriopathy may represent chronic active ABMR42as well as TCMR—also shown in experimental studies43—and that chronic active TCMR may also be manifest in the tubulointerstitial compartment.

Table 4 Banff lesion grading system

Continued Table 4

During the postmeeting discussion， it was clearly articulated that further studies are needed to understand the significance of i-IFTA in the context of chronic active TCMR before i-IFTA can be included as a diagnostic criterion. In particular， the ongoing work of the borderline/TCMR BWG is expected to generate relevant data in this context.

Prospects for Adopting Molecular Pathology in Renal Allograft Diagnosis

As part of the 2013 revision of the Banff classification for diagnosing ABMR， molecular assessment of transcripts indicative of endothelial injury in the renal allograft biopsy was added as a potential diagnostic criterion1； however， there is no consensus on which transcripts are diagnostic or on the criteria for positivity.Standards for platforms， methods， and reproducibility for such molecular diagnostic assays have not yet been set； such standards are a requirement for robust clinical validation and adoption in diagnostic pathology laboratories. During the 2015 Banff premeeting on“Precision Diagnostics in Transplantation，” current knowledge in the area of molecular transplant diagnostics was reviewed. State-of- the-art presentations on molecular diagnostics in allograft biopsies and body fluids revealed that significant commonalities exist with regard to the molecular phenotype in transplant biopsies from different organ types44. In addition,overlap exists with molecular signatures found in body fluids45. In contrast, there is considerableheterogeneity among published studies with regard to how the molecular phenotype has been assessed and applied as a potential diagnostic and/or predictive tool46.Over the last decade， transplant biopsies， blood，and urine have been studied comprehensively，primarily using transcriptomics， and have led to novel insights into the molecular phenotypes of organ transplants47-53. Current ongoing studies—for example， the INTERCOM studies47-48—are assessing a molecular microscope approach in real time for examining kidney allograft biopsies and comparing the gene expression classifiers and diagnosis to the current gold standard histopathology. This represents a step forward and will generate important results to help guide integration of molecular analysis with morphology. Accordingly， at the 2015 Banff meeting，converging opinion was supported by recent data50，53that molecular transplantation pathology is at the point where it can be translated into clinically relevant and applicable diagnostic tools. The obstacles to be overcome lie in （i） the lack of a true diagnostic gold standard against which new molecular diagnostics can be compared and calibrated （there is no gold standard for serology or histology either）； （ii） the fact that data have been generated from heterogeneous cohorts with diagnostic labels assigned based on different iterations of the Banff classification； （iii）the absence of completed prospective， controlled，randomized validation studies； and （iv） the lack of agreement on the transcripts to be measured and how to measure them.

Most disease processes operating in organ transplants represent a spectrum of certain biological processes.Accordingly， our current diagnostic criteria （e.g.for TCMR and ABMR） are built on semiquantitative diagnostic thresholds of lesions associated with a certain phenotype. Such thresholds aim to represent the optimal trade-off between side effects of enhanced treatment （i.e. overimmunosuppression） and the detrimental impact of further disease progression（i.e. underimmunosuppression）. A potential path forward would be to generate consensus in molecular transplant diagnostics regarding which molecules are assessed or quantified in what settings（Table 5） and then to develop clinically relevant diagnostic thresholds through retrospective and prospective multicenter validation studies based on standardized assessment of the same molecular lesions in the same clinical context. This approach would be analogous to the Banff consensus process in 1991 for morphologic lesions.Previous research revealed strong associations between certain molecular pathways and well-established Banff histologic lesions （Figure 1）. These key molecular pathways can be represented and thus assessed by relatively few molecules from each pathway， either through quantification of respective gene sets or through summarizing such genes in weighted equations as diagnostic classifiers. Generating consensus for sets of molecules or classifiers reflecting certain biological or disease processes related to the established histologic Banff lesions would enable us to assess and validate their clinical value. In this regard， the most robust evidence is currently available for the association among antibody-mediated injury； microcirculation inflammation； and increased expression of endothelial，NK cell， and inflammation-associated transcripts in the allograft29，54-56.

Table 5 Key areas for which consensus needs to be generatedand validated to adopt molecular diagnostics into the Banff classification

Figure 1 Molecular lesions and their corresponding histologic lesions in T cell-mediated rejection and antibody-mediated rejection in kidney allografts. cg， glomerular double contours；cv，vascular fibrous intimal thickening；i，inflammation；ptc，peritubular capillaritis；ti，total inflammation ； v，intimal arteritis.

Discussion of the above approach took place at the 2015 Banff meeting and continued afterward via e-mail exchange among the key opinion leaders. From these interactions， key next steps toward adopting molecular diagnostics into transplantation pathology were identified and are summarized （Table 6）：

Table 6 Identified knowledge gap in the adoption process for molecular transplant diagnostics

1. The overwhelming majority of those who commented support pursuing the generation of molecular consensus gene sets （or classifiers） from the overlap between published gene lists， adding key genes based on pathogenesis-based association with the main clinical indications and phenotypes （TCMR， ABMR）.

2. More collaborative multicenter studies are needed（Table 6） to close existing knowledge gaps before Banff can “officially” adopt specific molecular diagnostics as part of the classification.

3. Consensus must be generated on gene sets， which can be studied further in a multicenter setting.

4. Results from such studies should be reviewed at future Banff meetings as part of an ongoing consen- sus process for molecular diagnostics.

Once consensus for gene sets and/or classifiers for molecular biopsy assessment is achieved， prospective and retrospective validation trials can be initiated.Similar to the validation of histologic Banff lesions and diagnostic rules established in 1991， only multicenter validation of different diagnostic approaches with hard clinical end points （e.g. allograft survival， response to treatment） can establish clinically useful diagnostic thresholds. In the absence of a true diagnostic gold standard， adoption of molecular diagnostics can only be accomplished in a stepwise and iterative approach over time including constant revisiting and refinement of current molecular consensus as new knowledge emerges.

Summary of the Banff Pancreas Session

Three main topics （Table 7） were emphasized at the pancreas transplant session： （i） discussion of controversial morphologic aspects， （ii） progress made with the working groups since the 2013 meeting，and （iii） encouragement of data regarding the utility of endoscopic duodenal cuff biopsies as surrogates of biopsies of the pancreas transplant. Data were presented showing that a normal duodenal cuff biopsy accurately predicts absence of TCMR in the pancreas parenchyma. A study of duodenal cuff biopsies showed a high incidence of cytomegalovirus infection in these samples that we do not know how to interpret at this stage. Furthermore， data from detailed morphologic studies on pale acinar nodules in native and transplant pancreas biopsies， which are still of unclear etiology and clinical significance，were presented57. A study was presented at the Banff session that showed simultaneous pancreas and kidney transplant biopsies demonstrating high concurrence between acute ABMR in both organs and significant discrepancy between organs for TCMR. Modifications to the Banff pancreas allograft pathology schema were made after consensus was reached following e-mail circulation to the BWG for Pancreas Pathology and via discussions during the meeting. Main updates include incorporation of acute ABMR grading， improved definitions for TCMR and ABMR， specifica tion of vascular lesions， and inclusion of b cell islet toxicity in the category of islet pathology. In the second part of the session， key opinion leaders discussed morphologic and clinical aspects of graft loss in whole pancreas transplants as well as islet transplantation. It was concluded that better understanding of the etiology of graft loss represents an unmet need. This will require systematic integration of morphologic （pathology），serologic （DSAs and autoantibodies）， and clinicalfunctional （e.g. oral glucose tolerance test） parameters for studying the cause and incidence of pancreas transplant failure.

Summary of the VCA Session

The VCA session included speaker presentations and discussion. Focal points of the former were ABMR after face transplantation58， graft vasculopathy in the skin59， cutaneous changes among transplant patients，and the expansion of the Banff VCA scoring system.The discussion included challenges to the Banff VCA system， immunohistochemistry markers， specimen adequacy， and differential diagnoses. Collaborative efforts were discussed， and the working group concentrated on the standardization of a document for the retrospective and prospective collection of data.The group will reconvene at an international workshop on VCA histopathology with the goals of continuing discussions of the refinement of the Banff VCA system， the standardized form， and the development of a consensus document that would be accessible worldwide. The goal is to compile data and to review it at the Banff 2017 meeting.

Table 7 Updated Banff pancreas allograft rejection grading schema

Continued Table 7

Acknowledgments

We would like to acknowledge the instrumental support from the Roche Organ Transplantation Research Foundation Grant 608390948 awarded to Dr. Kim Solez， which allowed establishing the Banff Foundation for Allograft Pathology. The joint 2015 Banff and Canadian Transplant Society meeting acknowledges the receipt of sponsorship from Astellas， Alexion，Novartis， One Lambda， Renal Pathology Society，American Society of Transplantation， Wiley， Qiagen，Canadian Institute for Health Research， Immucor，Bridge to Life， Organ Recovery Systems， Transplant Connect， Glycorex Transplantation， Transpath Inc.，and the University of Alberta.

Disclosure

The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation.

Supporting Information

Additional Supporting Information may be found in the online version of this article.

Data S1 ：The Banff Manual： Definitions and Rules

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第十三屆Banff會議在加拿大溫哥華舉行，來自28個國家的共計451名病理學家、免疫學家、臨床及外科專家參加本次會議。會議首先回顧分析了2013年修改的抗體介導性排斥（antibodymediated rejection，ABMR）診斷標準對臨床的影響，隨后，指出了目前Banff診斷標準存在的一定局限性并討論將“分子診斷”引入分類標準的前景。會議對Banff工作組（Banff work group， BWG）的工作進行總結(jié)和規(guī)劃，指出：BWG在連續(xù)4次的工作會議中制定和修改了包括孤立性動脈炎、初始移植物質(zhì)量，纖維化、供腎活檢、多瘤病毒、C4d陰性的ABMR以及腎小球病變等診斷及分類的具體標準，因此，會議決定暫停上述小組的工作?！案咧旅艋颊摺惫ぷ鹘M，提出了關(guān)于免疫調(diào)節(jié)/脫敏、活檢時間以及人類白細胞抗原（human leukocyte antigen， HLA）抗體和供者特異性抗體（donor specific antibody， DSA）水平相關(guān)報告 ；“TCMR”工作組報告了研究情況和主要目標（原文表2），預計將在2017年Banff會議上提供新的結(jié)論。本次會議形成4個新BWG，包括“血栓性微血管病變”、“復發(fā)性腎小球疾病”、“電子顯微鏡診斷”和“綜合替代終點”。 BWG的最終目標是整合病理學和相關(guān)生物標志物，建立一個綜合評分系統(tǒng)，以預測移植物長期結(jié)果。新BWG的目標、領導者、初步結(jié)果和正在進行的工作（原文表2）。BWG的創(chuàng)始人Kim Solez認為“組織工程病理學”是一個嶄新的病理學，可能會在未來發(fā)揮更大的作用。

1 排斥反應診斷和分類的新挑戰(zhàn)

會議期間對ABMR、T細胞介導的排斥（T-cell mediated rejection， TCMR）和混合性排斥的診斷進行了討論，提出由于ABMR的臨床表現(xiàn)具有異質(zhì)性，會給診斷帶來困難。美國組織相容性和免疫遺傳學協(xié)會（American Society for Histocompatibility and Immunogenetics， ASHI）提出了對DSA檢測結(jié)果以及其在Banff分類中的解釋(原文表2），表明在非高致敏患者中，新發(fā)DSA在亞臨床的ABMR具有重要意義，因此，有必要加強對亞臨床ABMR的觀察以及對治療效果的評估，進一步明確其臨床意義。由于多重微珠陣列的抗體檢測的進展，提高了對循環(huán)DSA檢測的敏感性和準確性，發(fā)現(xiàn)并非所有的DSA都具有同等效應，除了DSA的陽性和強度之外，DSA的性質(zhì)（結(jié)合補體或IgG亞型的能力）和預先存在或復發(fā)以及新生的抗體與損傷存在關(guān)聯(lián)，這些現(xiàn)象在其他實體器官移植（肝臟、心臟）中得到證實。報告中還提到DSA的持續(xù)時間、動力學和性質(zhì)具有波動性，因此，在單個時間點（特別是移植后期），對于檢測結(jié)果的解釋應謹慎。由于非抗HLA-DSA可以單獨或與抗HLADSA共同對移植物造成損傷，因此，在僅有ABMR相關(guān)的病理表現(xiàn)（如微循環(huán)炎癥、C4d沉積和血管炎）而沒有DSA結(jié)果時ABMR能否被診斷仍需討論。此外，在腎移植中，特別是與新發(fā)DSAs相關(guān)的晚期病例，ABMR可以混合TCMR共同存在，在出現(xiàn)微血管炎和動脈內(nèi)膜炎的活檢中也常常出現(xiàn)小管/間質(zhì)性TCMR的病變，這些病例可能代表混合性ABMR和TCMR，通常對單一的ABMR或TCMR治療無效。會議認為移植腎小球病 （transplant glanerulopathy， TG）患者是否需要接受積極的抗ABMR治療，特別是存在DSA的患者中，應該取決于是否伴有活動性MVI。

2 針對HLA或其他抗原的DSA對ABMR診斷的影響

Banff 2013分類標準中提出：針對HLA或其他抗原的DSA可作為急/慢性活動性ABMR診斷的血清學證據(jù)。然而，腎小管周圍毛細血管的C4d沉淀，是DSA高度特異指證，本次會議對DSA和腎小管周圍毛細血管C4d染色作為診斷ABMR的必要性進行了討論，多數(shù)研究者認為目前的數(shù)據(jù)不能證實，進而增加“活檢符合組織學診斷標準和腎小管周圍毛細血管C4d的染色陽性的患者有極大可能診斷ABMR，但需要進一步行DSA檢測”并總結(jié)了新的診斷標準（原文表3）。DSASTs在DSA陽性和陰性患者中表達差異在許多中心被證實，因此，DSASTs可識別哪些未檢測出HLA DSA的ABMR患者。目前，轉(zhuǎn)錄模式、抗HLA Ⅰ類和Ⅱ類、 平均熒光強度，補體/非補體結(jié)合抗體以及不同IgG亞類等對不同DSA患者預后的影響有待進一步研究。

3 慢性活動性TCMR與間質(zhì)纖維化和腎小管萎縮區(qū)域的炎癥

Banff標準對慢性活動TCMR僅列出血管病變（單個核細胞浸潤纖維化動脈），這既不完整也不準確，提出并討論了間質(zhì)纖維化和腎小管萎縮區(qū)域的炎 癥（interstitial inflammation in areas of interstitial fibrosis and tubular atrophy， i-IFTA）應作為慢性活動性TCMR的潛在病變，應作為Banff病變評分一部分，并依據(jù)i-IFTA占皮質(zhì)纖維化區(qū)域分為輕度（≤25%）、中度（26%～50%）和重度（＞50%），需要注意的是i-IFTA和i評分標準于不一致，其炎癥評估是以纖維化區(qū)域為主。

4 分子病理學在腎移植診斷中的前景

在2013 ABMR Banff診斷標準中提出了內(nèi)皮損傷的分子學評估可作為潛在標準，但由于目前對于分子診斷的標準化平臺、方法和可重復性尚未建立，因此，尚未達成診斷共識。在會議前的“移植精準醫(yī)療”討論中，對目前分子學領域進行了綜述，研究提示不同器官移植組織的分子表型存在共性，而且在體液中發(fā)現(xiàn)重疊的分子指征，但以現(xiàn)有研究結(jié)論尚難以作為一個潛在的評估和應用標準。利用轉(zhuǎn)錄組學在活檢、血液和尿液進行了全面研究，發(fā)現(xiàn)了器官移植中的新的分子表型，有助于指導分子分析與形態(tài)學的整合。目前，移植分子/病理學研究轉(zhuǎn)化為臨床診斷工具還解決一些難題。當前的診斷標準（例如，TCMR和ABMR）是建立在與某種表型相關(guān)的病變的半定量診斷閾值上，未來方向是在分子診斷中產(chǎn)生共識（原文表5），然后，通過基于相同分子標準化評估的回顧性和前瞻性多中心驗證研究，在相同的臨床背景下明確臨床相關(guān)的診斷閾值。某些分子途徑和組織學病變之間的關(guān)聯(lián)（見原文圖1），最有力的證據(jù)可用于抗體介導的損傷之間的關(guān)聯(lián)，微循環(huán)炎癥以及內(nèi)皮細胞，NK細胞和炎癥相關(guān)轉(zhuǎn)錄物在同種異體移植物中的表達增加。在沒有真正的診斷“金標準“下，分子診斷的采用只能在逐步完成，包括新知識的出現(xiàn)和對當前分子共識的不斷認識和優(yōu)化。

5 胰腺和血管化復合同種異體移植物（vascularized composite allograft，VCA）

胰腺移植會議討論了形態(tài)學、工作進展和內(nèi)窺鏡活檢3個主題（原文表7），提出十二指腸套囊活檢能夠準確地預測胰腺實質(zhì)中TCMR和發(fā)現(xiàn)巨細胞病毒（cytomegaoviyns virus， CMV）感染率很高。對自體和移植胰腺的淡然腺泡結(jié)節(jié)進行了詳細的形態(tài)學描述，但仍然不清楚其病因和臨床意義。研究表明，胰腺和腎臟聯(lián)合移植后的活檢顯示兩種器官急性ABMR之間是高度一致，TCMR存在顯著差異。對胰腺移植病理學診斷模式進行了修改，包括急性ABMR分級，完善TCMR和ABMR的定義、血管損傷定義以及胰島細胞病理學中胰島B細胞毒性的研究（原文表5）。通過形態(tài)學（病理學），血清學（DSA和自身抗體）和臨床功能（例如口服葡萄糖耐量試驗）參數(shù)的統(tǒng)一結(jié)合來研究胰腺移植失敗的原因和發(fā)生率，這樣可以更好地理解移植失

VCA重點討論了面部移植后的ABMR、血管病變、皮膚變化以及Banff VCA評分系統(tǒng)的擴充，包括免疫組織化學標志物、樣本充足性和鑒別診斷。工作組將繼續(xù)討論Banff VCA系統(tǒng)的改進，采用標準化的形式，制定可獲得共識的文件及數(shù)據(jù)并在2017年Banff會議上進行審定。