Review Recommended Treatment for Antibody-mediated Rejection After Kidney Transplantation: The 2019 Expert Consensus From the Transplantion Society Working Group Carrie A. Schinstock, MD,1 Roslyn B. Mannon, MD,2 Klemens Budde, MD,3 Anita S. Chong, PhD,4 Mark Haas, MD,5 Stuart Knechtle, MD,6 Carmen Lefaucheur, MD, PhD,7 Robert A. Montgomery, MD,8 Peter Nickerson, MD,9 Stefan G. Tullius, MD, PhD,10 Curie Ahn, MD, PhD,11,12 Medhat Askar, MD, PhD,13 Marta Crespo, MD, PhD,14 Steven J. Chadban, PhD,15 Sandy Feng, MD, PhD,16 Stanley C. Jordan, MD,17 Kwan Man, PhD,18 Michael Mengel, MD,19 Randall E. Morris, MD,20 Inish O’Doherty, PhD,21 Binnaz H. Ozdemir, MD, PhD,22 Daniel Seron, MD, PhD,23 Anat R. Tambur, PhD,24 Kazunari Tanabe, MD, PhD,25 Jean-Luc Taupin, PhD,26,27 and Philip J. O’Connell, PhD28 Abstract. With the development of modern solid-phase assays to detect anti-HLA antibodies and a more precise histo- logical 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. (Transplantation 2020;104: 911–922). INTRODUCTION sensitive solid-phase assays to detect donor-specific anti- Despite modern immunosuppression, ongoing kidney HLA antibodies (DSA) and the development of the Banff injury and graft loss due to alloantibody-induced immu- diagnostic criteria for antibody-mediated rejection (AMR), nity remains an important issue.1-4 Driving this response has the size of the problem been realized. By 10 years, after are polymorphic HLA antigens. While the impact of kidney transplant, up to 25% have developed de novo antibodies to HLA on kidney allograft survival has been DSA (dnDSA).5 Thus, it is not surprising that AMR was known for some time, only recently, with the advent of the most common cause of allograft failure in a cohort of Received 7 October 2019. Revision received 20 November 2019. 6 Duke Transplant Center, Department of Surgery, Duke University School of Accepted 3 December 2019. Medicine, Durham, NC. 7 C.A.S. and R.B.M. are equal first author. Université de Paris, Department of Transplantation, Saint Louis Hospital, Paris, 1 Mayo Clinic William J. von Liebig Center for Transplantation and Clinical France. 8 Regeneration, Mayo Clinic, Rochester, MN. NYU Langone Transplant Institute, New York, NY. 2 9 Division of Nephrology, University of Alabama at Birmingham, Birmingham, AL. Transplant Immunology Laboratory, Shared Health and Rady Faculty of Health 3 Department of Nephrology and Medical Intensive Care, Charité Sciences, University of Manitoba, Winnipeg, MB, Canada. 10 Universitätsmedizin Berlin, Berlin, Germany. Division of Transplant Surgery and Transplant Surgery Research Laboratory, 4 Section of Transplantation, Department of Surgery, The University of Chicago, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA. 11 Chicago, IL. Transplantation Center, Seoul National University Hospital, Seoul, Korea. 5 12 Department of Pathology and Laboratory Medicine, Cedars-Sinai Medical Department of Internal Medicine, Seoul National University College of Center, Los Angeles, CA. Medicine, Seoul, Korea. Transplantation ■ May 2020 ■ Volume 104 ■ Number 5 www.transplantjournal.com 911 912 Transplantation ■ May 2020 ■ Volume 104 ■ Number 5 www.transplantjournal.com renal transplant recipients with indication biopsies before BIOLOGY OF THE ALLOIMMUNE RESPONSE graft failure.3 Moreover, in a multicenter cohort study, A general appreciation of the complex immunologic antibody-mediated damage caused allograft dysfunction processes underlying antibody production in immuno- late posttransplant in nearly 60% of renal transplant logically naive and presensitized individuals is central to recipients.4 understanding the varied presentations of AMR and poten- Given the scope and severity of the problem, it is tial treatment options (Figure 1). In alloimmune naive indi- unfortunate that there are no commonly accepted guide- viduals, the generation of antibody-secreting cells follows lines for treatment. To date, clinical trials of AMR have a scripted series of checkpoint events, starting with the been small or inconclusive, and there are no Federal initial encounter of alloantigen with B cells expressing the Drug Administration (FDA)-approved therapies for the appropriate B-cell antigen receptor. This event activates prevention and treatment of the condition.6 The lack of B-cell migration to the T- and B-cell interface in the lymph an accepted common standard for the treatment of AMR node, where it receives help from alloreactive T cells that has been an impediment to the development of new ther- encountered alloantigen presented indirectly on recipient apies because it is difficult for industry to initiate phase dendritic cells. Some of B cells differentiate into memory 2 and 3 clinical trials for novel treatments or preven- B cells or short-lived plasmablasts, while the rest enter tion of AMR. To overcome this lack of evidence-based into germinal centers to emerge as high-affinity and class- guidelines, The Transplantation Society brought together switched memory B cells, plasmablasts, and long-lived a group of experts from around the globe for a 1.5-day plasma cells.7,8 In the context of transplantation, presen- meeting, with the aim of producing a consensus docu- sitized individuals have a robust long-lived plasma cells ment that outlined recommended treatments for active constitutively secreting anti-HLA antibodies and resting and chronic active AMR, based on the best available evi- memory B cells primed to secrete large amounts of anti- dence. This publication is a summary of that meeting and body upon antigen reexposure leading to a rapid anamnes- includes up-to-date information about the pathogenesis tic antibody response. of the condition, the criteria for diagnosis, prognosis, and Some features of the alloimmune response complicate long-term outcome. our understanding of DSA production, limiting our ability 13 Baylor University Medical Center, Transplant Immunology, Dallas, TX. 14 ViroPharma and AstraZeneca. He received honoraria for serving as a speaker Department of Nephrology, Hospital del Mar and Institute Hospital del Mar for and advisor for CareDx and Novartis. M.M. has research funding from Roche Medical Research, Barcelona, Spain. Diagnostics and advisory board membership from Novartis and Vitaeris. C.L. 15 Department of Renal Medicine, Royal Prince Alfred Hospital, Sydney, Australia. has a research grant from CSL Behring. R.A.M. served on advisory boards for 16 Department of Surgery, University of California San Francisco, San Francisco, CA. Genentech Scientific/ROCHE, Alexion, Novartis, CSL Behring, eGenesis, Sanofi, 17 Viela Bio, Vitaeris Bio, and Hansa Medical. He received consulting fees or travel Comprehensive Transplant Center, Cedars-Sinai Medical Center, West expenses from Alexion, Hansa Medical, CLS Behring, Viela Bio, Vitaeris Bio, Hollywood, CA. and Shire/Takeda. He received research grants from ViroPharma/Shire, Hansa 18 Department of Surgery, The University of Hong Kong, Hong Kong, People's Medical, United Therapeutics, and Alexion. P.N. is a consultant for Vitaeris Inc., Republic of China. Astellas Pharma, Vielo Bio, Paladin, and Renalytix AI Inc. and received honoraria 19 Department of Laboratory Medicine and Pathology, University of Alberta, from Astellas and Thermo Fisher Scientific. Edmonton, AB, Canada. M.A. is an advisory board member for Immucor. S.J.C. has received travel 20 Stanford University School of Medicine, Stanford, CA. support, speakers fees, or advisory board payments from Novartis, Astellas, 21 Vitaeris, Alexion, and AstraZeneca. S.F. is an advisory board member for Critical Path Institute, Tucson, AZ. Novartis. S.C.J. is a consultant for CSL Behring, Vitaeris, and Hansa Medical 22 Department of Pathology, Baskent University, School of Medicine, Ankara, Turkey. and has received research grants from CSL Behring, Vitaeris, and Hansa 23 Nephrology Department, Hospital Vall d’Hebron, Autonomous University of Medical. I.O. works for the Critical Path Institute that received funding from the Barcelona, Catalonia, Spain. FDA and member companies. D.S. received grants from Astellas, TEVA, and 24 Chiesi and is an advisory board member for Astellas, Novartis, CSL Behring, Comprehensive Transplant Center, Northwestern University, Chicago, IL. and Vitaeris. A.R.T. is an advisory board member for Astellas and Viela Bio and 25 Department of Urology, Tokyo Women’s Medical University, Tokyo, Japan. is the central lab for HLA testing for an Astellas study. The other authors declare 26 Laboratory of Immunology and Histocompatibility, Hôpital Saint-Louis APHP, no conflicts of interest. Paris, France. P.J.O. proposed and organized the meeting and was primarily responsible 27 INSERM U976 Institut de Recherche Saint-Louis, Université Paris Diderot, for the development of the program and overall editing of the manuscript. Paris, France. C.A.S. and R.B.M. delivered presentations at the meeting, were involved in 28 discussion, and undertook a major role in writing the manuscript. K.B., A.S.C., Centre for Transplant and Renal Research, Westmead Institute of Medical M.H., S.K., C.L., R.A.M., P.N., and S.G.T. were responsible for writing sections Research, University of Sydney and Renal Unit, Westmead Hospital, NSW, of the manuscript. All other authors either delivered presentations or chaired Australia. sessions, were involved in discussions, and participated in the development of This meeting was organized by The Transplantation Society with the assistance the consensus. All authors reviewed and edited the manuscript and agreed with of an unconditional education grant from CSL Behring. CSL Behring had no the final document. involvement in the development of the program, the choice of speakers, nor in Correspondence: Philip J. O’Connell, MBBS, PhD, Centre for Transplant and the writing of the manuscript. The manuscript was written by the authors. Renal Research, Westmead Institute of Medical Research, Westmead, NSW P.J.O. is an advisory board member for CSL Behring, eGenesis, Qihan Biotech, 2145, Australia. (philip.oconnell@sydney.edu.au). and Renalytix AI and received research funding from CSL Behring. C.A.S. involved Copyright © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. This in current contracts with CSL Bering and negotiating research contracts with is an open-access article distributed under the terms of the Creative Commons Vitaeris. R.B.M. has received research grants from CSL Behring, Alexion, and Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it Mallinckrodt and honoraria from Novartis and Hansa. He serves on the Medical is permissible to download and share the work provided it is properly cited. The Steering Committee for Vitaeris Imagine Trial. K.B. has received research funds work cannot be changed in any way or used commercially without permission and honoraria from Abbvie, Alexion, Astellas, Bristol-Meyer Squibb, Chiesi, from the journal. CSL, Behring, Fresenius, Genetech, Hexal, Novartis, Otsuka, Pfizer, Roche, Shire, Siemens, Veloxis, and Vitaeris. M.H. serves as a paid consultant on ISSN: 0041-1337/20/1045-911 pathology adjudication committees for industry-sponsored clinical trials by Shire DOI: 10.1097/TP.0000000000003095 © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. Schinstock et al 913 FIGURE 1. Kinetics of memory B cells and plasma cell generation relative to the germinal center (GC) reaction following transplantation. Following encounter with alloantigen, activated B cells migrate to the T- and B-cell interface and receive T-cell help. Some of the helped B cells differentiate into memory B cells or plasma cells, while the rest enter into a germinal center to emerge as high-affinity and class- switched memory B cells and plasma cells. Memory B cells tend to have low levels of somatic hypermutations and lower B-cell receptor (BCR) affinity compared with plasma cells, and cells generated pre-GC tend to be of lower affinity than cells generated post-GC. to predict and develop therapeutic approaches for AMR. In MVI in the form of glomerulitis (g) and peritubular capil- general, memory B cells are derived from B cells with recep- laritis (ptc). The presence of either (g + ptc > 0) satisfies tors that are less mutated and of lower affinity than those criterion 1, and a (g + ptc) sum score of ≥2 also satisfies that are destined to become plasma cells.9-11 As a result, the criterion 2. The exception is that peritubular capillari- repertoire of plasma cells and memory B cells are not iden- tis alone is insufficient for diagnosis in the presence of tical. Furthermore, the repertoire of plasma cells and the T-cell–mediated rejection (TCMR), including borderline antibodies they produce are up to 100-fold more restricted rejection. Recurrent or de novo glomerulonephritis must compared with the repertoire of memory B cells.12 These be considered as a differential diagnosis, especially in the differences between memory B cells and plasma cell genera- context of glomerulitis and thrombotic microangiopathy. tion predict that treatment aiming to prevent plasma cell To diagnose chronic active AMR, morphological features generation and subsequent DSA production may not stop of chronic tissue injury are present in addition to crite- the generation of memory B cells. Likewise, the absence of ria 2 and 3 for active AMR. Signs of chronic tissue injury DSA does not imply the lack of memory B cells and the include transplant glomerulopathy (Banff chronic glomer- potential for an anamnestic response. Thus, the ability to ulitis [cg] score > 0), severe peritubular capillary basement quantify donor-specific memory B cells may aid in risk membrane multilayering on electron microscopy, or new stratification and treatment of presensitized recipients sus- arterial intimal fibrosis without another obvious cause. ceptible for an active AMR early posttransplant. The diversity at the level of antibodies presents an CLINICAL PHENOTYPES OF AMR additional challenge. Antibodies have different Fc regions corresponding to their isotype and subclasses, each with The Banff classification has been a major advancement in nonoverlapping functions including their ability to bind the field of transplantation to increase the awareness of AMR to Fc receptors and activate complement. Less appreci- and standardize definitions. However, a classification schema ated is heterogeneity in the anti-HLA antibody repertoire, based on histological features oversimplifies the complexity which comprise antibodies that bind to private specifici- of AMR. The Banff classification has 3 AMR diagnostic cat- ties on HLA molecules and thus are highly donor specific. egories (including chronic AMR with transplant glomeru- Alternatively, cross-reactive alloantibodies may be donor lopathy and current or prior DSA but no MVI or C4d): the reactive but not donor specific, and some may bind mul- clinical reality is that AMR is frequently a chronic progres- tiple HLA molecules. As a result, the breadth of the circu- sive disease process. This chronic disease process starts with lating antibody with HLA reactivity may not be a direct the formation of DSA. The DSA may or may not lead to readout of the plasma cell repertoire. active AMR with histological features that often include but are not limited to MVI. Moreover, not all active AMR will progress to chronic active AMR. Over time, chronic histo- DIAGNOSTIC CRITERIA AND HISTOLOGICAL logical features such as transplant glomerulopathy become FEATURES OF AMR evident, and eventually, the patient develops allograft dys- AMR is a clinicopathological diagnosis that was function, proteinuria, and probable allograft loss. Thus, find- first formally described in a 2003 addition to the 1997 ing an active versus chronic active AMR on the biopsy may International Banff Classification of kidney allograft rejec- be more reflective of the timing of the biopsy rather than the tion13 but has continually evolved with our increased underlying pathological process itself. understanding of AMR particularly with regards to the Further complicating the diagnosis and management of relevance of C4d-negative AMR and the utility of molecu- AMR are various clinical phenotypes. AMR can present lar diagnostics. The salient features of active AMR based with abrupt allograft dysfunction early posttransplant but on the Banff 2017 classification14 are (1) histological can also have an insidious or subclinical onset, presenting evidence of graft injury via microvascular inflammation later posttransplant. Anti-HLA antibody can also be pre- (MVI), intimal or transmural arteritis (v > 0), acute throm- sent before transplant (preexisting DSA) or develop after botic microangiopathy in the absence of any other cause, transplant (dnDSA) in the setting of under-immunosuppres- or acute tubular injury in the absence of any other appar- sion. In some circumstances, the histological features sug- ent cause; (2) histological evidence of antibody-endothelial gestive of AMR are present, but anti-HLA antibody is not interactions either by C4d deposition or at least moderate detected. Incorporating these clinical features of AMR into MVI; and (3) the presence of circulating DSA, predomi- the current Banff classification while considering the likely nantly anti-HLA antibody (Table 1). Clearly, the main his- underlying immunologic mechanisms is critical to appro- tological manifestation of active AMR in renal allografts is priately guide therapeutic decisions and ultimately design 914 Transplantation ■ May 2020 ■ Volume 104 ■ Number 5 www.transplantjournal.com TABLE 1. Banff 2017 classification of AMR in renal allografts14 Active AMR All 3 criteria must be met for diagnosis 1 Histological evidence of acute tissue injury, including 1 or more of the following: (a) Microvascular inflammation (g > 0 or ptc > 0), in the absence of recurrent or de novo glomerulonephritis. In the presence of acute T-cell–mediated rejection, borderline infiltrate, or infection, ptc >1 alone is not sufficient. (b) Intimal or transmural arteritis (v > 0) (c) Acute thrombotic microangiopathy, in the absence of any other cause (d) Acute tubular injury, in the absence of any other apparent cause 2 Evidence of current/recent antibody interaction with vascular endothelium, including 1 or more the following: (a) Linear C4d staining in peritubular capillaries (C4d2 or C4d3 by immunofluorescence on frozen sections, or C4d >0 by IHC on paraffin sections) (b) At least moderate microvascular inflammation ([g + ptc] ≥2) in the absence of recurrent or de novo glomerulonephritis, although in the presence of a T-cell–mediated rejection, borderline infiltrate, or infection, ptc ≥2 alone is not sufficient. (c) Increased expression of gene transcripts/classifiers in the biopsy tissue strongly associated with AMR, if thoroughly vali- dated. 3 Serological evidence of donor-specific antibodies (DSA to HLA or other antigens); C4d staining or expression of validated tran- scripts/classifiers as noted in criterion 2 may substitute for DSA Chronic active Morphological evidence of chronic tissue injury, including 1 or more the following, plus criteria 2 and 3 for Active AMR: AMR Transplant glomerulopathy (cg >0) if no evidence of chronic thrombotic microangiopathy or chronic recurrent/de novo glo- merulonephritis; includes changes evident by electron microscopy alone Severe peritubular capillary basement membrane multilayering on electron microscopy Arterial intimal fibrosis of new onset, excluding other causes AMR, antibody-mediated rejection; cg, chronic glomerulitis; DSA, donor-specific antibody; g, glomerulitis; IHC, immunohistochemistry; ptc, peritubular capillaritis; v, vasculitis score. efficient and effective therapeutic clinical trials. Therefore, Late (>30 Days) Posttransplant AMR With we recommend considering the timing of presentation, and Preexisting DSA type of DSA (preexisting or de novo), in relation to the his- While many patients with preexisting DSA do not tological classification as discussed below (Table 2). develop an aggressive early AMR as described above, they can develop an indolent and progressive form of AMR that Early Posttransplant (<30 Days) Active AMR is usually initially detected on a surveillance biopsy (in the In patients who have measurable DSA at the time of setting of stable function) or on a for-cause biopsy for mild kidney transplant or who have an immunologic amnes- allograft dysfunction.42,43 Histological findings are depend- tic response due to previous exposure to allo-HLA, active ent on the timing of the biopsy. When detected early, MVI AMR can occur within the first 30 days posttransplant. in glomeruli and peritubular capillaries is the predominant The risk of early posttransplant AMR increases with finding and C4d staining may or may not be present. MVI growing DSA strength or breadth at the time of transplant tends to persist and is later accompanied by chronic his- as determined by DSA mean fluorescence intensity (MFI), tological features including transplant glomerulopathy and the degree of flow cytometric crossmatch positivity, and peritubular basement membrane multilayering.17,44,45 At the number or breadth of cross-reactive DSA specifici- diagnosis, there is often minimal if any reduction in glomer- ties.15,16 In general, this form of AMR is uncommon, as it ular filtration rate (GFR) or proteinuria even when mild is common practice to avoid allocating kidneys to patients chronic features are present. Overtime, however, the GFR with known preformed DSA, as early posttransplant AMR declines and the patient becomes proteinuric39 with graft occurs in up to 40% of patients with preformed DSA and failure often occurring several years after transplant.18,21 In a positive flow cytometric crossmatch.38,39 This aggres- an observational prospective cohort study of >100 renal sive form of active AMR typically presents with an abrupt transplant recipients who underwent surveillance biopsy at increase in DSA accompanied by allograft dysfunction 1 year, patients with AMR were the most likely to experi- (increased creatinine and oliguria with or without pro- ence allograft failure.21 Allograft survival was only 56% at teinuria). If not recognized and treated quickly, it can lead 8 years posttransplant compared with 88% if subclinical to cortical necrosis and allograft loss within days. From TCMR was present, and 90% if the biopsy was normal.21 a histological perspective, the criteria for Banff active AMR are met and C4d is usually positive.40 There is often Late (>30 Days) AMR Associated With dnDSA interstitial hemorrhage, glomerular fibrin thrombi, and In the current era of sensitive DSA testing and a general microvascular coagulative necrosis. With prompt diagno- avoidance of preexisting DSA, the most common form of sis and treatment, patients can recover allograft function AMR is associated with dnDSA. In general, dnDSA is a new and histological features of active AMR frequently resolve DSA detected after >3 months posttransplant in the context of completely.40,41 In other cases, the histological features of inadequate immunosuppression which is either due to patient active AMR persist and chronic active AMR, allograft dys- nonadherence, physician directed, or genetically determined function, and ultimate allograft failure ensues. variability in metabolism of immunosuppressive drugs. This TABLE 2. Antibody-mediated rejection phenotypes Timing DSA Histologya Clinical presentation Pathophysiology Prognosis Features associated with reduced allograft survival a Early Acute Preexisting DSA Banff 2017 active AMR Abrupt allograft dysfunction Memory B-cell Graft loss Pretransplant crossmatch (+T-AHG-CDC+15 or high-flow cytometric (<30 days (or nonimmuno­ Usually C4d+ correlating with increased response within crossmatch)15 posttransplant) logically naive) Thrombotic microangiopathy DSA MFI or titer usually days if not often present 7–10 days posttransplant15 treated15 Late (>30 days Preexisting DSA Banff 2017 active or ± Allograft dysfunction and Preexisting plasma Graft loss Histological © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. posttransplant) chronic active AMR proteinuria cell response within Banff cg >0 lesion19,21,22 May be C4d± months to Degree of IFTA23-25 16-20 ys Concomitant TCMR22-24,26,27 De novo DSA Banff 2017 active or ± allograft dysfunction and Under-immuno­ Graft loss Banff cv score >024 chronic active AMR proteinuria suppression within C4d positivity28-30 May be C4d± months Clinical Concomitant TCMR to ys Proteinuria19,25,31,32 often present 28-30,32 Allograft dysfunction19,22,24,25,31,33 Ys posttransplant24,25 Patient nonadherence or physician-directed immunosuppression reduction22,25 DSA characteristics C1q-positive DSA24,34,35 High DSA MFI or titer and pretransplant crossmatch16,18,31,36,37 Anticlass II DSA17,36 a Hyperacute rejection is associated with very high DSA (positive complement-dependent cytotoxicity crossmatch) at the time of transplant and results in graft loss within minutes to hours posttransplant. This type of AMR is virtually nonexistent in the current era and not addressed in this article. AMR, antibody-mediated rejection; CDC, complement-dependent cytotoxicity; cg, chronic glomerulitis; cv, chronic vasculopathy; DSA, donor-specific antibody; IFTA, interstitial fibrosis and tubular atrophy; MFI, mean fluorescence intensity; TCMR, T-cell mediated rejection. Schinstock et al 915 916 Transplantation ■ May 2020 ■ Volume 104 ■ Number 5 www.transplantjournal.com form of AMR often presents with allograft dysfunction and antibody screening, and obtaining a history of allosensi- concomitant or preexisting TCMR.3,46,47 In patients who tizing events (previous transplant, blood transfusion, and have routine surveillance DSA testing or surveillance biopsies, pregnancy) (strength of recommendations and level of evi- the presentation can be more indolent and is similar to that dence 1A).54-56 Molecular HLA typing ideally includes A; of late posttransplant AMR in patients with preexisting DSA B; C; DRB1; DRB3, 4, 5; DQA1/DQB1; and DPA1/DPB1 (subclinical AMR associated with dnDSA).46 (2B). For anti-HLA–sensitized recipients, a high-resolution Results from 2 recent studies have suggested that AMR level of typing, approaching or even reaching the allelic with dnDSA is associated with inferior allograft survival level (ie, the so-called “4-digit” typing), should be under- when compared with AMR from preexisting DSA after taken as often as possible on the potential donor, to match adjusting for clinical, histological, and immunologic char- the resolution of the alloantibody identification assays. acteristics.19,23 Allograft survival was 63% in patients with The first-line screening for alloantibody would be with preexisting DSA and only 34% in patients with dnDSA single-antigen bead (SAB) solid-phase assays (LABScreen 8 years after the rejection diagnosis.19 Despite these find- [one Lambda] or LifeScreen [LifeCodes-Immucor]), but ings, it remains unclear whether it is the dnDSA itself that multiantigen beads can also be used (1A). Patients with is associated with inferior allograft survival or a delay in no history of allosensitizing events and with negative anti- AMR diagnosis. Compared with patients with preexisting HLA antibody testing using single-antigen or multiantigen DSA, those with dnDSA tend to have increased proteinuria bead solid-phase assays are at low risk for AMR. and increased expression of interferon-γ–inducible, natu- ral killer cell, and T-cell transcripts at presentation.19 Monitoring for De Novo DSA Immunosuppression reduction either as a result of non- FEATURES ASSOCIATED WITH REDUCED adherence or under physician direction is associated with ALLOGRAFT SURVIVAL IN LATE AMR development of dnDSA.46,47,51 Monitoring for dnDSA is (PREEXISTING OR DNDSA) recommended in the following settings: immunosuppres- Although there are differences in the initial presentation of sion reduction by physician for any reason, known patient AMR and pace of clinical deterioration depending on whether medication nonadherence, or at the time of rejection epi- the DSA is formed before the transplant, or is dnDSA, the his- sode (T cell or antibody mediated) (2B). The presence of tological, clinical, and alloantibody features associated with dnDSA is a general indicator of under-immunosuppression reduced allograft survival are similar (Table 2). Allograft and signals the need to reevaluate maintenance immu- histology is key to document the chronicity and extent of nosuppression. Based on the strong relationship between injury. Chronic histological features such as the presence of dnDSA, AMR, and graft loss, transplant patients with transplant glomerulopathy (Banff cg score >0)19,21,22 and the dnDSA should undergo close monitoring of allograft func- degree of interstitial fibrosis and tubular atrophy23-25 are pre- tion19,22,47 (1B). A kidney biopsy is also recommended to dictive of allograft failure. Other histological features asso- detect T-cell or AMR (clinically evident or subclinical).6 ciated with inferior allograft survival include concomitant TCMR,22-24,26,27 C4d positivity,28-30,48 and vascular lesions Interpreting Positive DSA Results (Banff cv score >0).24 Not surprisingly, clinical factors are The SAB test detecting DSA has been an important also predictive of outcome including allograft dysfunction advancement to the field; however, the test has limitations at diagnosis,19,22,24,25,31,49 proteinuria,19,25,31,32 and time of that must be identified for correct interpretation. First, the diagnosis posttransplant.24,25 To illustrate the relevance of SAB test has a high coefficient of variation, and thus, the posi- having allograft dysfunction at presentation: time to 50% tive cutoff varies among and within laboratories. In general, graft failure was 3.3 years in patients with allograft dysfunc- a positive cutoff MFI of 1000–1500 is associated with the tion versus 8.3 years in patients without allograft dysfunc- detection of specific anti-HLA antibodies.57 SAB tests are also tion among 47 patients with dnDSA.22 Although it is clear prone to interference from external substances, bead satura- that under-immunosuppression is a major risk factor for tion, and “shared-epitope” phenomenon, which can lead to a dnDSA, prior studies have also shown that a history of medi- falsely low MFI.53,58,59 Methods to identify interference and cation nonadherence is independently associated with infe- bead saturation include performing serum dilution or using rior allograft survival among patients with dnDSA.22,25,50,51 ethylenediaminetetraacetic acid. We recommend the routine Lastly, several alloantibody characteristics have been use of these methods in the following situations: transplant associated with outcome including the presence of C1q- candidates/recipients who are not immunologically naive, positive DSA34,35,52 and anticlass II DSA.17,36 Additionally, unexpected positive crossmatch, or AMR with unexpectedly the level or strength of DSA correlates with graft failure low DSA MFI (2B). as determined by DSA titer or flow cytometric crossmatch positivity. Notably, several studies have correlated DSA Additional DSA Testing for Risk Stratification titer and MFI with C1q positivity53; thus, it is unclear All patients with DSA are at some risk for AMR. whether complement binding characteristics or levels of Crossmatch testing can be used with SAB testing for AMR alloantibody determine outcomes. risk stratification. The risks of AMR from highest to low- est based on crossmatch and SAB-positive testing are the following: positive complement-dependent cytotoxicity CONSENSUS FOR MEASURING AND MONITORING (CDC) crossmatch, positive flow cytometric crossmatch, OF DSA and negative crossmatch.60 Importantly, hyperacute AMR Initial Assessment for Anti-HLA DSA is also associated with having a positive CDC crossmatch. The initial assessment of a renal transplant candidate Testing to assess the complement binding ability of DSA involves donor and recipient HLA typing, anti-HLA (C1q or C3d) is commercially available, and positive results © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. Schinstock et al 917 are associated with AMR and allograft loss.34,52 However, expert consensus at the FDA Antibody-Mediated Rejection C1q and C3d binding positivity is associated with a high Workshop in 201767 as well as Kidney Disease: Improving DSA titer.53 It remains unclear whether complement bind- Global Outcomes (KDIGO) in 201068 was that PLEX and ing assays outperform antibody titers for AMR risk strati- IVIG could be regarded as a standard of care for acute active fication. For this reason, we do not recommend routine use AMR, despite the weakness of evidence in support of efficacy. of complement binding assays unless it is used as a means In particular, their ability to improve short-term outcomes of predicting high strength DSA. Lastly, DSA IgG subclass has been demonstrated by several studies,65,66,70,71 while testing has been used for research purposes. This testing their results on long-term effects remain variable, emphasiz- has not been thoroughly validated for clinical use and at ing the need for new alternatives or adjunctive therapy for the moment cannot be recommended. the treatment of AMR. In addition, there is a need to better define the amount of PLEX and dosing of IVIG. The rationale for using PLEX and IVIG is to combine AVAILABLE EVIDENCE FOR THE TREATMENT OF removal of circulating DSA with immunomodulation of the ACTIVE AND CHRONIC ACTIVE AMR antigraft immune response and in particular modulation Most reports on the treatment of AMR are small and of the B-cell response. In experimental models, IVIG has include heterogeneous patient populations. These studies been shown to inhibit B-cell responses by the Fc portion frequently include mixed antibody and TCMRs, do not dif- of the Ig binding the Fc fragment of IgG2b receptor on B ferentiate responses based on the timing of AMR detection, cells, and sialylated IVIG binds CD22, inducing apoptosis and make no distinction between dnDSA and preformed of mature B cells.72 It also functions as a scavenger of acti- DSA, although all these factors have an impact on out- vated complement.72 While PLEX and IVIG have formed come.61 The heterogeneity of available studies makes it diffi- the mainstay of treatment for acute active AMR, the evi- cult to draw meaningful conclusions about treatment effects. dence consists largely of case series and poorly controlled As recommended by guidelines,56 most studies describe the randomized trials. Well-designed clinical trials in this use of a variable mix of interventions (eg, variable intensity area have proven difficult. One of the best-designed trials of plasmapheresis, different doses of intravenous immune recruited only 10 patients (5 in each arm) and consisted of globulins [IVIG], variable use of steroid pulses together with immunoabsorption without IVIG. While all of the patients or without different T-cell–depleting and B-cell–depleting receiving immunoabsorption responded to treatment, the antibodies). Obviously, these different interventions create a trial was ceased at the first interim analysis because of 80% challenge in the interpretation of treatment effects. As a con- graft loss in the control arm, which suggests that immuno- sequence, treatment studies for AMR are rarely comparable, absorption was beneficial in this setting.71 and the available evidence is generally of low quality.55,62 Complement Inhibitors Plasma Exchange and IVIG Over the last decade, the complement system has The primary aims of nearly all therapeutic approaches attracted increasing attention as an important contributor for AMR are removing circulating DSA and reducing DSA to AMR. Hence, several studies have been undertaken to production. In this sense, the strongholds for contemporary evaluate the ability of various complement inhibitors to treatment of AMR are represented by plasma exchange prevent and treat AMR. The main goal of using comple- (PLEX) and IVIG, although neither of these have FDA ment inhibitors is to avoid the downstream damage to the approval. This treatment regimen is most commonly used allograft from DSA. to treat active AMR, although frequency, modality, and dos- Eculizumab results in terminal complement blockade ing may vary14,55,56,61,62 (Table 3). On those grounds, the as a monoclonal antibody targeting C5. A single-center TABLE 3. Evidence for use of plasma exchange and intravenous immune globulins as SOC in active AMR Criterion Evidence Reference Biological rationale Anti-HLA antibodies activate complement and interact with Fc receptors and endothelium. Akiyoshi et al63 Removal of anti-HLA Ab via plasma exchange correlates with better clinical response in kidney Gelfand64 transplant recipients. Intravenous immune globulins have pleiotropic effects including neutralization of antibodies/ cytokines/activated components of complement, effects on B cells, T cells, and Fc receptors. Benefit in clinical Humoral rejection treated with PE/IVIG results in improved renal function. Rocha et al65 (observational) The combination PE/IVIG leads to better removal of anti-HLA antibodies and correlates with better Lefaucheur et al66 studies graft survival. International FDA 2017 Public workshop: Antibody removal therapies, generally in combination with low- or Velidedeoglu et al67 recommendations high-dose IVIG (immunomodulation) form the SOC in many institutions. Kasiske et al68 KDIGO 2010: Recommendation for PE and IVIG in association with corticosteroids. Most used combination American Society of Transplantation survey: Most centers utilize a combination of IVIG and plas- Burton et al69 in clinical practice mapheresis for treatment. Roberts et al55 The treatment of AMR in kidney transplant recipients: a systematic review. Ab, antibody; AMR, antibody-mediated rejection; Fc, fragment crystallizable; IVIG, intravenous immune globulins; PE, plasma exchange; FDA, Federal Drug Administration; KDIGO, Kidney Disease: Improving Global Outcomes; SOC, standard of care. 918 Transplantation ■ May 2020 ■ Volume 104 ■ Number 5 www.transplantjournal.com study showed that among patients who received positive rebound as part of a desensitization protocol in highly crossmatch HLA-incompatible transplants, the incidence sensitized patients.82 However, optimal doses, number of early active AMR was decreased from approximately of treatment cycles, and the effect on patients without 40% in historical controls to 7% among treated patients. a vascular component remain unclear, as is the need for Furthermore, 2 multicenter randomized phase 2 trials con- Rituximab within a multimodal regimen.83 firmed the protective effect of eculizumab for preventing early active AMR in positive crossmatch HLA-incompatible Imlifidase living73 and deceased74 donor populations. A single-center Imlifidase (Hansa Biopharma AB), an IgG-degrading small case series has also shown that eculizumab has effec- enzyme of Streptococcus pyogenes (IdeS), can rapidly tiveness in treating early active AMR that occurs within reduce or even eliminate anti-HLA DSA and is undergo- the first month posttransplant.40 Despite these promising ing clinical trials in AMR.84 IdeS cleaves human IgG at a results, long-term follow-up of eculizumab-treated posi- highly specific amino acid sequence within the hinge region tive crossmatch patients in a single-center study has shown producing Fc and F(ab)2 fragments and effectively block- that despite prevention of early active AMR, the long-term ing CDC and antibody-dependent cellular cytotoxicity.85 incidence of chronic AMR and allograft survival is compa- Although data are lacking for using IdeS in AMR, this rable to historical controls.18,45 agent has been used safely in highly sensitized individuals Proximal complement inhibition has also been studied for desensitization. After administration of IdeS, all previ- as a therapeutic target. The plasma C1 esterase inhibi- ously positive crossmatches became negative and all stud- tors Berinert (CSL Behring) and Cinryze (Takeda/Shire/ ied patients received a transplant.86 Unfortunately within ViroPharma) have been tested in 2 pilot studies and indi- 7–10 days of administration, patients often experience a cate a possible improvement in allograft function in kid- rebound in DSA and anti-IdeS antibodies develop after 1 ney recipients with AMR.75,76 An additional clinical trial or 2 doses, thereby preventing repeated administrations. evaluating a C1 esterase inhibitor for the treatment of Thus, IdeS will unlikely be an isolated treatment for active AMR that is resistant to PLEX and IVIG (NCT03221842) or chronic active AMR, but rather an adjunct to other ther- in renal transplant recipients is ongoing. apies aiming to reduce DSA in the long term. The unique feature of this drug is that it permits any highly sensitized Rituximab patient to undergo transplantation within hours of a donor Rituximab, a B-cell–depleting agent, was suggested as a being identified regardless of the crossmatch status. treatment option by KDIGO guidelines.56 Despite its fre- quent use,69 the evidence is low and 3 small randomized Antithymocyte Globulin trials have investigated its utility without demonstrating Since its introduction, antithymocyte globulin (ATG) a clear benefit.55,62,77 A small study in 20 children inves- or other T-cell–depleting antibodies have been used for tigated the effect of Rituximab compared with standard treatment of refractory rejection, vascular rejection, mixed of care (pulse steroids) in B-cell–rich rejections (of whom rejections, and AMR.69,87 Although depleting antibodies 40% in the control group and 80% in treatment group were proposed by KDIGO guidelines as potential treatment had DSA).78 There were no major differences in outcome, options,56 no benefit has been demonstrated for treatment and Rituximab had a reasonable safety profile. However, of pure AMR with T-cell–depleting therapy.55,62,87 No pro- small numbers, demographic, and baseline differences as spective trial with ATG for AMR had been performed, and well as an unclear AMR definition preclude meaningful a large retrospective series suggests that T-cell depletion in conclusions. The second trial was a French prospective, combination with steroids has no effect on the outcome double-blind, multicenter, randomized study investigating in vascular AMR.81 Side effects are well described with 38 patients with active AMR in the first year after trans- a higher risk of infectious-associated death, particularly plantation. All patients received treatment with steroids, when ATG was combined with B-cell depletion.88 IVIG, and PLEX and were randomized to either rituxi- mab or placebo. There was no difference in any outcome Splenectomy parameter, except side effects.79 More recently, there was a Spanish prospective, randomized, placebo-controlled, dou- There are several case series of surgical splenectomy, ble-blinded clinical trial where patients were randomized splenic embolization, and splenic radiation being used as a to receive IVIG plus Rituximab or IVIG plus saline infu- salvage procedure for severe early AMR.89,90 It must be per- sion. Only 50% enrollment was achieved (25 patients), formed rapidly after the onset of early AMR to be effective. and at 12 months, there were no differences between treat- Designing a proper study would be challenging and patients ment and control groups in estimated glomerular filtration who have undergone splenectomy are known to be sensi- rate decline, level of proteinuria, Banff score on biopsy, or tized, have preformed antibody, or have undergone desen- MFI of the immunodominant DSA.80 In contrast to these sitization therapy. Most of these AMR cases occur in the prospective RCTs, several retrospective analyses have sug- first week after transplantation and result in profound graft gested some positive effects of rituximab in multimodal dysfunction and a sudden rise in DSA strength, usually from treatment regimens together with steroids, plasmapher- an anamnestic response. Some patients who recover develop esis, and high-dose IVIG, especially on patients with vas- transplant glomerulopathy and premature graft loss. cular AMR.55,62,81 A recent study developed a prognostic score on the basis of a treatment response to a regimen Proteasome Inhibitor: Bortezomib with Rituximab in the context of multimodal therapy. Bortezomib is a proteasome inhibitor approved for Moreover, a single-center nonrandomized study suggests the treatment of multiple myeloma that directly targets that Rituximab as an add-on therapy may prevent DSA antibody-producing plasma cells making it an attractive © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. Schinstock et al 919 candidate for the treatment of active AMR.91 Data sup- the combination of PLEX, IVIG with corticosteroids could porting its use are limited to case series suggesting a posi- be regarded as standard of care, consistent with the con- tive effect within a multimodal treatment regimen of clusions of the FDA workshop and KDIGO guidelines PLEX, IVIG, steroids, and depleting antibodies.55,62,91 The (Table 4).6,56 However, in some centers, the use of corticos- only prospective randomized, double-blind, placebo-con- teroids is reserved for patients with concompetant TCMR. trolled trial was in “late” AMR and did not demonstrate While adjunctive therapy with other agents has been used any beneficial effect of bortezomib alone.92 The drug has in specific settings, there have been only 3 (underpow- well-documented side effects, and at the present time, there ered) prospective randomized trials for treatment of active are no trial data to support its use.93 AMR.78,79,92 These trials had many limitations, and most evidence comes from small retrospective studies with dif- Cyclophosphamide ferent combination therapies using different AMR defini- Cyclophosphamide is used for the treatment of antibody- tions in different populations.40,55,62,83 Thus, the available mediated diseases such as anti-neutrophil cytoplasmic anti- evidence supporting the use of any adjunctive agents is of body vasculitis or lupus nephritis. Previous anecdotal reports low quality with the best evidence relating to drug toxicity describe its use within a multimodal treatment regimen for and costs. Nevertheless, these rejections are relatively rare the treatment of refractory rejections.62,94 While it is rela- with a high incidence of graft loss and a randomized clini- tively inexpensive, there are no trial data to support its use. cal trial would be difficult to achieve. Hence, in the absence of trial data, the consensus was that adjunctive therapy Interleukin-6 Inhibitors may be warranted especially when the risk of graft loss A single-center, nonrandomized trial of tocilizumab is considered high. The recommended adjunctive therapies (anti-interleukin-6 receptor monoclonal antibody) was include complement inhibitors, rituximab, or splenectomy undertaken in 36 patients with chronic active AMR that depending on availability (Table 4). Where concomitant had failed IVIG plus rituximab. Patient and graft survival TCMR is present, it should be treated. at 6 years (91% and 80%, respectively) were found to be superior to historical controls, with significant reductions CONSENSUS FOR TREATMENT OF LATE in DSA and stabilization of renal function.95 Partly based ACTIVE AND CHRONIC ACTIVE AMR (≥30 DAYS on these encouraging results, a small investigator-initiated POSTTRANSPLANT) randomized control trial has begun recruitment and a large multicenter randomized control trial has been initiated to Preexisting DSA evaluate Clazakizumab, an anti-interleukin-6 monoclonal As described above, the transition from active to chronic antibody, for the treatment of chronic active AMR.96 active AMR should be considered a continuum, and the DSA may have been present at the time of transplant or CONSENSUS FOR TREATMENT OF EARLY ACTIVE appear de novo. Among patients with known preexisting AMR (≤30 DAYS POSTTRANSPLANT) DSA and active AMR without chronic features, the con- The current evidence for treatment options in active sensus treatment recommendations include PLEX, IVIG, AMR is of limited quality. The consensus view was that and corticosteroids. TABLE 4. Consensus treatment recommendations based on available evidence and expert opinion Histology Consider adjunctive Timing DSA (Banff 2017) Standard of carea therapies Earlya Acute Preexisting DSA (or Active AMR Plasmapheresis (daily or alternative day × 6 based on Complement inhibitors (2B) (<30 days nonimmunologi- DSA titer) (1C)b Rituximab 375 mg/m2 (2B) posttransplant) cally naive) IVIG 100 mg/kg after each plasmapheresis treatment or Splenectomy (3C) IVIG 2 g/kg at end of plasmapheresis treatments (1C) Corticosteroids (EO) Late (>30 days Preexisting DSA Active AMR Plasmapheresis (daily or alternative day × 4–6 based on Rituximab 375 mg/m2 (2B) posttransplant) DSA titer) (2C)b IVIG 100 mg/kg after each plasmapheresis treatment or IVIG 2 g/kg at end of plasmapheresis treatments (2C) Corticosteroids (EO) Chronic AMR Optimize baseline immunosuppression (eg, add steroids if IVIG (3C) on a steroid-free regimen) (1C) De novo DSA Active AMR Optimize baseline immunosuppression (eg, add steroids if Plasmapheresis and IVIG (3C) on a steroid-free regimen) (1C) Rituximab (3C) Evaluate and manage nonadherence Chronic AMR IVIG (3C) a For all cases, treatment of concomitant T-cell–mediated rejection (≥borderline) and optimizing immunosuppression is recommended. Optimizing immunosuppression includes the use of tacrolimus with goal trough of >5 and use of maintenance steroid equivalent to prednisone 5 mg daily. b Fresh-frozen plasma to be used for replacement fluid for plasmapheresis if a biopsy was performed within 24–48 h. The codes for grades of evidence have been taken from KDIGO.54,56 AMR, antibody-mediated rejection; DSA, donor-specific antibody; EO, expert opinion; IVIG, intravenous immune globulins; KDIGO, Kidney Disease: Improving Global Outcomes. 920 Transplantation ■ May 2020 ■ Volume 104 ■ Number 5 www.transplantjournal.com In cases of chronic active AMR or chronic transplant 4. Gaston RS, Cecka JM, Kasiske BL, et al. Evidence for antibody- mediated injury as a major determinant of late kidney allograft failure. vasculopathy, goals of therapy should be to stabilize or Transplantation. 2010;90:68–74. reduce the rate of decline in GFR, proteinuria, histological 5. Everly MJ, Rebellato LM, Haisch CE, et al. Incidence and impact injury score, and titer of DSA while minimizing drug toxic- of de novo donor-specific alloantibody in primary renal allografts. ity. The use of IVIG and PLEX, with or without Rituximab, Transplantation. 2013;95:410–417. 6. Archdeacon P, Chan M, Neuland C, et al. Summary of FDA Antibody- has not been shown to improve outcomes in patients with Mediated Rejection Workshop. Am J Transplant. 2011;11:896–906. chronic active AMR (as distinct from acute active AMR) 7. Kurosaki T, Kometani K, Ise W. Memory B cells. Nat Rev Immunol. and has to be balanced against increased risk of adverse 2015;15:149–159. events such as infection and cost. The consensus opinion 8. Nutt SL, Hodgkin PD, Tarlinton DM, et al. The generation of antibody- secreting plasma cells. Nat Rev Immunol. 2015;15:160–171. was that treatment should focus on optimizing immuno- 9. Sciammas R, Shaffer AL, Schatz JH, et al. Graded expression of inter- suppression and supportive care, with reintroduction of feron regulatory factor-4 coordinates isotype switching with plasma steroids (if on a steroid-free regimen), maintaining trough cell differentiation. Immunity. 2006;25:225–236. tacrolimus levels >5 ng/mL, and optimizing medical man- 10. Ochiai K, Maienschein-Cline M, Simonetti G, et al. Transcriptional regulation of germinal center B and plasma cell fates by dynamical agement with focus on blood pressure, blood glucose, and control of IRF4. Immunity. 2013;38:918–929. lipid control. 11. Shinnakasu R, Inoue T, Kometani K, et al. Regulated selection of ger- minal-center cells into the memory B cell compartment. Nat Immunol. De Novo DSA 2016;17:861–869. 12. Lavinder JJ, Horton AP, Georgiou G, et al. Next-generation sequenc- dnDSA generally occurs in the context of reduced immu- ing and protein mass spectrometry for the comprehensive analysis of nosuppression whether from patient nonadherence or a human cellular and serum antibody repertoires. Curr Opin Chem Biol. physician-directed change in immunosuppression. AMR in 2015;24:112–120. 13. Racusen LC, Solez K, Colvin RB, et al. The Banff 97 working clas- this setting is also often initially detected with concomi- sification of renal allograft pathology. Kidney Int. 1999;55:713–723. tant TCMR. Therefore, the standard for managing AMR 14. Haas M, Loupy A, Lefaucheur C, et al. The Banff 2017 Kidney Meeting in this setting (active or chronic active) is to optimize base- Report: revised diagnostic criteria for chronic active T cell-mediated rejection, antibody-mediated rejection, and prospects for integra- line immunosuppression and manage potential medica- tive endpoints for next-generation clinical trials. Am J Transplant. tion nonadherence. Treatment of concomitant TCMR is 2018;18:293–307. recommended in all cases of AMR but is particularly rel- 15. Gloor JM, Winters JL, Cornell LD, et al. Baseline donor-specific anti- evant in these cases. Similar to patients with chronic active body levels and outcomes in positive crossmatch kidney transplanta- tion. Am J Transplant. 2010;10:582–589. AMR in the context of preexisting antibodies, treatment 16. Schinstock CA, Gandhi M, Cheungpasitporn W, et al. Kidney trans- with PLEX, IVIG, and Rituximab is used in some centers, plant with low levels of DSA or low positive B-flow crossmatch: an although the evidence level (3C) is low. underappreciated option for highly sensitized transplant candidates. Transplantation. 2017;101:2429–2439. 17. Bentall A, Cornell LD, Gloor JM, et al. Five-year outcomes in living CONCLUSIONS donor kidney transplants with a positive crossmatch. Am J Transplant. Despite the severity of the problem and poor outcomes 2013;13:76–85. 18. Schinstock CA, Bentall AJ, Smith BH, et al. Long-term outcomes of for patients who develop AMR, there is very little high- eculizumab-treated positive crossmatch recipients: allograft survival, level evidence to support the use of any therapy. Most histologic findings, and natural history of the donor-specific antibod- trials in this area have been small investigator-initiated ies. Am J Transplant. 2019;19:1671–1683. 19. Aubert O, Loupy A, Hidalgo L, et al. Antibody-mediated rejection due studies with small numbers of participants, lacking appro- to preexisting versus de novo donor-specific antibodies in kidney allo- priate controls. As a result, there were no clear treatment graft recipients. J Am Soc Nephrol. 2017;28:1912–1923. regimens to recommend and there are no approved treat- 20. Amrouche L, Aubert O, Suberbielle C, et al. Long-term outcomes ments. The consensus opinion of those present at the meet- of kidney transplantation in patients with high levels of preformed DSA: the Necker high-risk transplant program. Transplantation. ing was based largely on observational studies, low-level 2017;101:2440–2448. evidence, and expert opinion. Despite the clear lack of evi- 21. Loupy A, Vernerey D, Tinel C, et al. Subclinical rejection phenotypes dence, it was considered important to define a standard of at 1 year post-transplant and outcome of kidney allografts. J Am Soc care for AMR, which could be used as a benchmark for Nephrol. 2015;26:1721–1731. 22. Wiebe C, Gibson IW, Blydt-Hansen TD, et al. Rates and determinants future studies and prospective trials. It is obvious that new of progression to graft failure in kidney allograft recipients with de novo agents and clinical trials are needed urgently. Future direc- donor-specific antibody. Am J Transplant. 2015;15:2921–2930. tions in this field will require new trial designs and large 23. Haas M, Mirocha J, Reinsmoen NL, et al. Differences in pathologic transnational trial consortia to undertake these studies.97 features and graft outcomes in antibody-mediated rejection of renal allografts due to persistent/recurrent versus de novo donor-specific In addition, better characterization of the different forms antibodies. Kidney Int. 2017;91:729–737. of AMR based on pathophysiology, histology, as well as 24. Viglietti D, Loupy A, Aubert O, et al. Dynamic prognostic score to clinical and genetic phenotypes is needed. predict kidney allograft survival in patients with antibody-mediated rejection. J Am Soc Nephrol. 2018;29:606–619. 25. Malheiro J, Santos S, Tafulo S, et al. Correlations between donor- REFERENCES specific antibodies and non-adherence with chronic active antibody- mediated rejection phenotypes and their impact on kidney graft 1. Meier-Kriesche HU, Ojo AO, Hanson JA, et al. Increased impact of survival. Hum Immunol. 2018;79:413–423. acute rejection on chronic allograft failure in recent era. Transplantation. 26. Krisl JC, Alloway RR, Shield AR, et al. Acute rejection clinically 2000;70:1098–1100. defined phenotypes correlate with long-term renal allograft survival. 2. El-Zoghby ZM, Stegall MD, Lager DJ, et al. Identifying specific causes Transplantation. 2015;99:2167–2173. of kidney allograft loss. Am J Transplant. 2009;9:527–535. 27. Matignon M, Muthukumar T, Seshan SV, et al. Concurrent acute 3. Sellarés J, de Freitas DG, Mengel M, et al. Understanding the causes cellular rejection is an independent risk factor for renal allograft of kidney transplant failure: the dominant role of antibody-mediated failure in patients with c4d-positive antibody-mediated rejection. rejection and nonadherence. Am J Transplant. 2012;12:388–399. Transplantation. 2012;94:603–611. © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. Schinstock et al 921 28. Loupy A, Hill GS, Suberbielle C, et al. Significance of C4D Banff 51. Schinstock CA, Dadhania DM, Everly MJ, et al. Factors at de novo scores in early protocol biopsies of kidney transplant recipients donor-specific antibody initial detection associated with allograft loss: with preformed donor-specific antibodies (DSA). Am J Transplant. a multicenter study. Transpl Int. 2019;32:502–515. 2011;11:56–65. 52. Bouquegneau A, Loheac C, Aubert O, et al. Complement-activating 29. Moktefi A, Parisot J, Desvaux D, et al. C1Q binding is not an inde- donor-specific anti-HLA antibodies and solid organ transplant survival: pendent risk factor for kidney allograft loss after an acute antibody- a systematic review and meta-analysis. Plos Med. 2018;15:e1002572. mediated rejection episode: a retrospective cohort study. Transpl Int. 53. Tambur AR, Herrera ND, Haarberg KM, et al. Assessing antibody 2017;30:277–287. strength: comparison of MFI, c1q, and titer information. Am J 30. Issa N, Cosio FG, Gloor JM, et al. Transplant glomerulopathy: risk and Transplant. 2015;15:2421–2430. prognosis related to anti-human leukocyte antigen class II antibody 54. Uhlig K, Macleod A, Craig J, et al. Grading evidence and recom- levels. Transplantation. 2008;86:681–685. mendations for clinical practice guidelines in nephrology. A position 31. Redfield RR, Ellis TM, Zhong W, et al. Current outcomes of chronic statement from kidney disease: improving global outcomes (KDIGO). active antibody mediated rejection - a large single center retrospec- Kidney Int. 2006;70:2058–2065. tive review using the updated BANFF 2013 criteria. Hum Immunol. 55. Roberts DM, Jiang SH, Chadban SJ. The treatment of acute anti- 2016;77:346–352. body-mediated rejection in kidney transplant recipients-a systematic 32. Naesens M, Lerut E, Emonds MP, et al. Proteinuria as a noninvasive review. Transplantation. 2012;94:775–783. marker for renal allograft histology and failure: an observational cohort 56. Kidney Disease: Improving Global Outcomes (KDIGO) Transplant study. J Am Soc Nephrol. 2016;27:281–292. Work Group. KDIGO clinical practice guideline for the care of kidney 33. Orandi BJ, Chow EH, Hsu A, et al. Quantifying renal allograft loss transplant recipients. Am J Transplant. 2009;9(Suppl 3):S1–S155. following early antibody-mediated rejection. Am J Transplant. 57. Reed EF, Rao P, Zhang Z, et al. Comprehensive assessment and 2015;15:489–498. standardization of solid phase multiplex-bead arrays for the detection 34. Loupy A, Lefaucheur C, Vernerey D, et al. Complement-binding of antibodies to HLA. Am J Transplant. 2013;13:1859–1870. anti-HLA antibodies and kidney-allograft survival. N Engl J Med. 58. Visentin J, Vigata M, Daburon S, et al. Deciphering complement inter- 2013;369:1215–1226. ference in anti-human leukocyte antigen antibody detection with flow 35. Bailly E, Anglicheau D, Blancho G, et al. Prognostic value of the beads assays. Transplantation. 2014;98:625–631. persistence of c1q-binding anti-HLA antibodies in acute antibody- 59. Tambur AR, Campbell P, Claas FH, et al. Sensitization in transplanta- mediated rejection in kidney transplantation. Transplantation. tion: assessment of risk (STAR) 2017 working group meeting report. 2018;102:688–698. Am J Transplant. 2018;18:1604–1614. 36. Willicombe M, Brookes P, Santos-Nunez E, et al. Outcome of 60. Montgomery RA, Warren DS, Segev DL, et al. HLA incompatible renal patients with preformed donor-specific antibodies following alem- transplantation. Curr Opin Organ Transplant. 2012;17:386–392. tuzumab induction and tacrolimus monotherapy. Am J Transplant. 61. Loupy A, Lefaucheur C. Antibody-mediated rejection of solid-organ 2011;11:470–477. allografts. N Engl J Med. 2018;379:1150–1160. 37. Lefaucheur C, Loupy A, Hill GS, et al. Preexisting donor-specific 62. Wan SS, Ying TD, Wyburn K, et al. The treatment of antibody-medi- HLA antibodies predict outcome in kidney transplantation. J Am Soc ated rejection in kidney transplantation: an updated systematic review Nephrol. 2010;21:1398–1406. and meta-analysis. Transplantation. 2018;102:557–568. 38. Vo AA, Peng A, Toyoda M, et al. Use of intravenous immune globu- 63. Akiyoshi T, Hirohashi T, Alessandrini A, et al. Role of comple- lin and rituximab for desensitization of highly HLA-sensitized patients ment and NK cells in antibody mediated rejection. Hum Immunol. awaiting kidney transplantation. Transplantation. 2010;89:1095–1102. 2012;73:1226–1232. 39. Stegall MD, Diwan T, Raghavaiah S, et al. Terminal complement inhibi- 64. Gelfand EW. Intravenous immune globulin in autoimmune and inflam- tion decreases antibody-mediated rejection in sensitized renal trans- matory diseases. N Engl J Med. 2012;367:2015–2025. plant recipients. Am J Transplant. 2011;11:2405–2413. 65. Rocha PN, Butterly DW, Greenberg A, et al. Beneficial effect of 40. Tan EK, Bentall A, Dean PG, et al. Use of eculizumab for active plasmapheresis and intravenous immunoglobulin on renal allograft antibody-mediated rejection that occurs early post-kidney trans- survival of patients with acute humoral rejection. Transplantation. plantation: a consecutive series of 15 cases. Transplantation. 2003;75:1490–1495. 2019;103:2397–2404. 66. Lefaucheur C, Nochy D, Andrade J, et al. Comparison of combi- 41. Orandi BJ, Zachary AA, Dagher NN, et al. Eculizumab and sple- nation plasmapheresis/IVIG/anti-CD20 versus high-dose IVIG in nectomy as salvage therapy for severe antibody-mediated rejec- the treatment of antibody-mediated rejection. Am J Transplant. tion after HLA-incompatible kidney transplantation. Transplantation. 2009;9:1099–1107. 2014;98:857–863. 67. Velidedeoglu E, Cavaillé-Coll MW, Bala S, et al. Summary of 2017 42. Loupy A, Hill GS, Jordan SC. The impact of donor-specific anti- FDA public workshop: antibody-mediated rejection in kidney trans- HLA antibodies on late kidney allograft failure. Nat Rev Nephrol. plantation. Transplantation. 2018;102:e257–e264. 2012;8:348–357. 68. Kasiske BL, Zeier MG, Chapman JR, et al; Kidney Disease: Improving 43. Gloor JM, Cosio FG, Rea DJ, et al. Histologic findings one year after Global Outcomes. KDIGO clinical practice guideline for the care of kid- positive crossmatch or ABO blood group incompatible living donor ney transplant recipients: a summary. Kidney Int. 2010;77:299–311. kidney transplantation. Am J Transplant. 2006;6:1841–1847. 69. Burton SA, Amir N, Asbury A, et al. Treatment of antibody-mediated 44. Wavamunno MD, O’Connell PJ, Vitalone M, et al. Transplant glomeru- rejection in renal transplant patients: a clinical practice survey. Clin lopathy: ultrastructural abnormalities occur early in longitudinal analy- Transplant. 2015;29:118–123. sis of protocol biopsies. Am J Transplant. 2007;7:2757–2768. 70. Montgomery RA, Zachary AA, Racusen LC, et al. Plasmapheresis 45. Cornell LD, Schinstock CA, Gandhi MJ, et al. Positive crossmatch and intravenous immune globulin provides effective rescue therapy kidney transplant recipients treated with eculizumab: outcomes for refractory humoral rejection and allows kidneys to be successfully beyond 1 year. Am J Transplant. 2015;15:1293–1302. transplanted into cross-match-positive recipients. Transplantation. 46. Wiebe C, Gibson IW, Blydt-Hansen TD, et al. Evolution and clinical 2000;70:887–895. pathologic correlations of de novo donor-specific HLA antibody post 71. Böhmig GA, Wahrmann M, Regele H, et al. Immunoadsorption in kidney transplant. Am J Transplant. 2012;12:1157–1167. severe c4d-positive acute kidney allograft rejection: a randomized 47. Schinstock CA, Cosio F, Cheungpasitporn W, et al. The value of proto- controlled trial. Am J Transplant. 2007;7:117–121. col biopsies to identify patients with de novo donor-specific antibody 72. Fehr T, Gaspert A. Antibody-mediated kidney allograft rejection: at high risk for allograft loss. Am J Transplant. 2017;17:1574–1584. therapeutic options and their experimental rationale. Transpl Int. 48. Orandi BJ, Alachkar N, Kraus ES, et al. Presentation and outcomes 2012;25:623–632. of c4d-negative antibody-mediated rejection after kidney transplanta- 73. Marks WH, Mamode N, Montgomery RA, et al; C10-001 Study tion. Am J Transplant. 2016;16:213–220. Group. Safety and efficacy of eculizumab in the prevention of anti- 49. Orandi BJ, Garonzik-Wang JM, Massie AB, et al. Quantifying the risk body-mediated rejection in living-donor kidney transplant recipients of incompatible kidney transplantation: a multicenter study. Am J requiring desensitization therapy: a randomized trial. Am J Transplant. Transplant. 2014;14:1573–1580. 2019;19:2876–2888. 50. Wiebe C, Nevins TE, Robiner WN, et al. The synergistic effect of class 74. Glotz D, Russ G, Rostaing L, et al; C10-002 Study Group. Safety II HLA epitope-mismatch and nonadherence on acute rejection and and efficacy of eculizumab for the prevention of antibody-mediated graft survival. Am J Transplant. 2015;15:2197–2202. rejection after deceased-donor kidney transplantation in patients 922 Transplantation ■ May 2020 ■ Volume 104 ■ Number 5 www.transplantjournal.com with preformed donor-specific antibodies. Am J Transplant. 86. Lonze BE, Tatapudi VS, Weldon EP, et al. Ides (imlifidase): a novel 2019;19:2865–2875. agent that cleaves human IgG and permits successful kidney trans- 75. Viglietti D, Gosset C, Loupy A, et al. C1 inhibitor in acute anti- plantation across high-strength donor-specific antibody. Ann Surg. body-mediated rejection nonresponsive to conventional therapy 2018;268:488–496. in kidney transplant recipients: a pilot study. Am J Transplant. 87. Bamoulid J, Staeck O, Crépin T, et al. Anti-thymocyte globulins in kid- 2016;16:1596–1603. ney transplantation: focus on current indications and long-term immu- 76. Montgomery RA, Orandi BJ, Racusen L, et al. Plasma-derived nological side effects. Nephrol Dial Transplant. 2017;32:1601–1608. C1 esterase inhibitor for acute antibody-mediated rejection fol- 88. Kamar N, Milioto O, Puissant-Lubrano B, et al. Incidence and predic- lowing kidney transplantation: results of a randomized double- tive factors for infectious disease after rituximab therapy in kidney- blind placebo-controlled pilot study. Am J Transplant. 2016;16: transplant patients. Am J Transplant. 2010;10:89–98. 3468–3478. 89. Locke JE, Zachary AA, Haas M, et al. The utility of splenectomy as 77. Macklin PS, Morris PJ, Knight SR. A systematic review of the use rescue treatment for severe acute antibody mediated rejection. Am J of rituximab for the treatment of antibody-mediated renal transplant Transplant. 2007;7:842–846. rejection. Transplant Rev (Orlando). 2017;31:87–95. 90. Kaplan B, Gangemi A, Thielke J, et al. Successful rescue of refractory, 78. Zarkhin V, Li L, Kambham N, et al. A randomized, prospective trial of severe antibody mediated rejection with splenectomy. Transplantation. rituximab for acute rejection in pediatric renal transplantation. Am J 2007;83:99–100. Transplant. 2008;8:2607–2617. 91. Ejaz NS, Alloway RR, Halleck F, et al. Review of bortezomib treat- 79. Sautenet B, Blancho G, Büchler M, et al. One-year results of the ment of antibody-mediated rejection in renal transplantation. Antioxid effects of rituximab on acute antibody-mediated rejection in renal Redox Signal. 2014;21:2401–2418. transplantation: RITUX ERAH, a multicenter double-blind randomized 92. Eskandary F, Regele H, Baumann L, et al. A randomized trial of bort- placebo-controlled trial. Transplantation. 2016;100:391–399. ezomib in late antibody-mediated kidney transplant rejection. J Am 80. Moreso F, Crespo M, Ruiz JC, et al. Treatment of chronic antibody Soc Nephrol. 2018;29:591–605. mediated rejection with intravenous immunoglobulins and rituximab: 93. Moreno Gonzales MA, Gandhi MJ, Schinstock CA, et al. 32 doses of a multicenter, prospective, randomized, double-blind clinical trial. Am bortezomib for desensitization is not well tolerated and is associated J Transplant. 2018;18:927–935. with only modest reductions in anti-HLA antibody. Transplantation. 81. Lefaucheur C, Loupy A, Vernerey D, et al. Antibody-mediated vascu- 2017;101:1222–1227. lar rejection of kidney allografts: a population-based study. Lancet. 94. Waiser J, Duerr M, Budde K, et al. Treatment of acute antibody-medi- 2013;381:313–319. ated renal allograft rejection with cyclophosphamide. Transplantation. 82. Vo AA, Lukovsky M, Toyoda M, et al. Rituximab and intravenous 2017;101:2545–2552. immune globulin for desensitization during renal transplantation. N 95. Choi J, Aubert O, Vo A, et al. Assessment of tocilizumab (anti- Engl J Med. 2008;359:242–251. interleukin-6 receptor monoclonal) as a potential treatment for 83. Budde K, Dürr M. Any progress in the treatment of antibody-mediated chronic antibody-mediated rejection and transplant glomerulopa- rejection? J Am Soc Nephrol. 2018;29:350–352. thy in HLA-sensitized renal allograft recipients. Am J Transplant. 84. Jordan SC, Lorant T, Choi J, et al. IgG endopeptidase in highly 2017;17:2381–2389. sensitized patients undergoing transplantation. N Engl J Med. 96. Eskandary F, Dürr M, Budde K, et al. Clazakizumab in late antibody- 2017;377:442–453. mediated rejection: study protocol of a randomized controlled pilot 85. Winstedt L, Järnum S, Nordahl EA, et al. Complete removal of extra- trial. Trials. 2019;20:37. cellular IgG antibodies in a randomized dose-escalation phase I study 97. OʼConnell PJ, Kuypers DR, Mannon RB, et al. Clinical trials for immu- with the bacterial enzyme ides–a novel therapeutic opportunity. PLoS nosuppression in transplantation: the case for reform and change in One. 2015;10:e0132011. direction. Transplantation. 2017;101:1527–1534.