Immunoassays's Posts (27)

  • O.O.Adebiyi, J.Gralla, P.Klem, B.Freed, S.Davis, A.C.Wiseman and J.E.Cooper

    Introduction
    The widespread utilization of single-antigen bead (SAB) assays prior to kidney transplantation has improved the detection of donor-specific antibody (DSA) in potential transplant recipients. Many studies have documented inferior renal graft outcomes in the presence of pretransplant DSA (1–15). However, the clinical importance of such DSA in the setting of a negative flow cytometry crossmatch (FCXM) at transplant remains controversial and the need for desensitization uncertain. There are limited published data regarding the impact of specific DSA characteristics such as class, strength or whether DSA persisted posttransplant on renal allograft outcomes when flow cytometry is negative. Additionally, the clinical significance of waxing/waning HLA antibodies pretransplant that are donor specific has not been reported in detail.
    The use of desensitizing agents prior to transplant for those patients at increased immunologic risk based on pretransplant screening has permitted successful transplantation for those who may not otherwise have had access to this treatment, despite higher acute rejection rates and inferior graft survival compared to those without preformed DSA (16,17). Clinical experience has shown these treatments to be necessary for patients with high-risk immunologic screening assays (complement-dependent cytotoxicity crossmatch [CDC] and/or FCXM positivity); however, the necessity of these costly therapies in the setting of SAB positivity alone remains uncertain, with practices varying center by center (17,18).
    Since September 2007, all renal transplant recipients at our center have undergone immunologic screening with both SAB and FCXM assays prior to transplantation. The aim of this study was to evaluate the impact of pretransplant DSA in the setting of negative FCXM screening on intermediate-term renal allograft outcomes in patients not receiving desensitization therapy. To our knowledge,this is the largest study of outcomes following kidney transplantation in the setting of low-level pretransplant DSA with negative FCXM to date.

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  • Dolores Redondo-Pachón, Julio Pascual, María J.Pérez-Sáez, Carmen García, Juan José Hernández, Javier Gimeno, Marisa Mir, Marta Crespoa

    The influence of antibodies against HLA-DP antigens detected with solid-phase assays on graft survival after kidney transplantation (KT) is uncertain.We evaluated with Luminex®the prevalence of pre- and posttransplant DP antibodies in 440 KT patients and their impact on graft survival. For 291 patients with available pretransplant samples, DP antibodies were present in 39.7% KT with pretransplant HLA antibodies and 47.7% with DSA. Graft survival of KT with pretransplant class-II DSA was worse than with non-DSA (p= 0.01). DP antibodies did not influence graft survival. Of 346 patients monitored post-KT, 17.1% had HLA class-II antibodies, 56% with DP antibodies. Class-II DSA was detected in 39%, 60.9% of them had DP antibodies. Graft survival was worse in patients with class-II DSA (p=0.022). DP antibodies did not change these results. The presence of isolated DP antibodies was a rare event both pre- and posttransplantation (1.03 and 0.86%). The presence of pretransplant and posttransplant DSA is associated with a negative impact on graft survival. However, the presence of DP antibodies does not modify this impact significantly.

    Keywords: Renal transplant, HLA-DP antibodies, Graft survival

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  • Craig J.Taylor, Vasilis Kosmoliaptsis, Jessie Martin, Graham Knighton, Dermot Mallon, J. Andrew Bradley, and Sarah Peacock

    Background. Solid-phase assays to distinguish complement binding from noncomplement binding HLA-specific antibodies have been introduced, but technical limitations may compromise their interpretation. We have examined the extent to which C1q-binding to HLA-class I single-antigen beads (SAB) is influenced by denatured HLA on SAB, antibody titre, and complement interference that causes a misleading low assessment of HLA-specific antibody levels. Methods. Sera from 25 highly sensitized patients were tested using Luminex IgG-SAB and C1q-SAB assays. Sera were tested undiluted, at 1:20 dilution to detect highlevel IgG, and after ethylene diamine tetraacetic acid treatment to obviate complement interference. Conformational HLA and denatured HLA protein levels on SAB were determined using W6/32 and HC-10 monoclonal antibodies, respectively. Denatured HLA was expressed as HC-10 binding to untreated SAB as a percentage of maximal binding to acid-treated SAB. Results. For undiluted sera, Luminex mean fluorescence intensity (MFI) values for IgG-SAB and C1q-SAB correlated poorly (r 2=0.42). ethylene diamine tetraacetic acid and serum dilution improved the correlation (r 2 = 0.57 and 0.77, respectively). Increasing levels of denatured HLA interfered with the detection of C1q binding. Consequently, the correlation between IgG-SAB MFI and C1q-SAB MFI was lowest using undiluted sera and SAB with greater than 30%denatured HLA (r2 = 0.40) and highest using diluted sera and SAB with 30% or less denatured HLA (r2 = 0.86). Conclusions. Antibody level, complement interference, and denatured HLA class I on SAB may all affect the clinical interpretation of the C1q-SAB assay. The C1q-SAB assay represents a substantial additional cost for routine clinical use, and we question its justification given the potential uncertainty about its interpretation.

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  • Glen P.Westall, and Greg I.Snell

    The lung transplant community continues to struggle with the diagnosis and management of antibody-mediated rejection. The four diagnostic tenets of donor-specific antibodies, C4d staining, histopathologic changes, and allograft dysfunction, which were largely derived from the early Banff meetings on renal transplantation, have somewhat arbitrarily been applied to lung transplantation. With the passage of time, it is increasingly apparent that merits of these diagnostic pillars are less robust in lung transplantation. In this article, we summarize some of the controversies and challenges surrounding the diagnosis of antibody-mediated rejection in lung transplantation.

    Keywords: Lung transplantation, Antibody-mediated rejection, Humoral rejection, Chronic lung allograft syndrome.

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  • M. Taniguchi, L.M.Rebellato, J.Cai, J.Hopfield, K.P.Briley, C.E.Haisch, P.G.Catrou, P.Bolin, K.Parker, W.T.Kendrick, S.A.Kendrick, R.C.Harland and P.I.Terasaki

    Reports have associated non-HLA antibodies, specifically those against angiotensin IItype-1receptor(AT1R), with antibody-mediated kidney graft rejection. However, association of anti-AT1R with graft failure had not been demonstrated. We tested anti-AT1R and donorspecific HLA antibodies(DSA) in pre-and posttransplant sera from 351 consecutive kidney recipients: 134 with biopsy-proven rejection and/or lesions (abnormal biopsy group [ABG]) and 217 control group (CG) patients. The ABG’s rate of anti-AT1R was significantly higher than the CG’s (18%vs. 6%, p<0.001). Moreover, 79% of ABG patients with anti-AT1R lost their rafts (vs. 0%, CG), anti-AT1R levels in 58% of those failed grafts increasing posttransplant. With anti-AT1R detectable before DSA, time to graft failure was 31 months—but 63 months with DSA detectable before anti-AT1R. Patients with both anti-AT1R and DSA had lower graft survival than those with DSA alone (log-rank p¼0.007). Multivariate analysis showed that de novo anti-AT1R was anindependent predictorof graft failure in theABG, alone (HR: 6.6), and in the entire population (HR: 5.4). In conclusion, this study found significant association of anti-AT1R with graft failure. Further study is needed to establish causality between anti-AT1R and graft failure and, thus, the importance of routine anti-AT1R monitoring and therapeutic targeting.

    Keywords: Angiotensin II type-1 receptor antibodies, AT1R, DSA, kidney transplantation, rejection

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  • Sarah Peacock, Vasilis Kosmoliaptsis, Andrew J.Bradley and Craig J.Taylor

    Luminex single antigen bead (SAB) technology enables highly sensitive and rapid characterization of immunoglobulin G (IgG) human leukocyte antigen (HLA)-specific antibodies. It is widely used to determine antibody compatibility for renal transplantation and to aid the diagnosis of antibody-mediated rejection and response to therapy. HLA-specific antibodies may contribute to allograft rejection through a variety of mechanisms, including activation of the classical complement pathway, endothelial cell activation, and recruitment of Fc-dependent effector cells. Of these, complement-mediated cytotoxicity has long been associated with hyperacute rejection and, more recently, antibody-mediated rejection for which the deposition of the complement component C4d on peritubular capillaries is a diagnostic marker. In the standard SAB assay, patient serum is incubated with microbeads coated with purified HLA proteins. Human leukocyte antigenYspecific IgG antibody binding is then detected using a fluorescent anti-IgG detection antibody. Increasing levels of donor HLA-specific antibodies detected by this assay predict inferior long-term graft outcome, but not all patients with IgG donor-specific HLA antibodies (DSA) have a poor graft outcome (1,2). This observation is consistent with the notion that HLA antibodies with the same specificity may differ in their ability to cause graft injury, and this variability may be related to differences in complement fixing activity.

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  • D.Thammanichanond, T.Mongkolsuk, S.Rattanasiri, S.Kantachuvesiri, S.Worawichawong, S.Jirasiritham and P.Kitpoka

    Objectives. De novo donor-specific HLA antibodies (DSA) are associated with allograft rejection and allograft loss. However, not all DSA are equally detrimental to allograft function. The ability to activate complement may be an important factor differentiating clinically relevant DSA from nonrelevant DSA. The C1q assay detects a subset of HLA antibodies that can fix complement. This study aimed to investigate the correlation between C1q-fixing de novo DSA (dnDSA) and clinical outcomes posttransplant.
    Methods. This retrospective study included 193 sera from kidney transplant recipients who underwent posttransplant DSA testing and/or kidney biopsy for clinical causes. Thirtyfive of the 193 (18.1%) had immunoglobulin G DSA. Seventeen of the 35 patients were excluded owing to the presence of pretransplant HLA antibodies. We then analyzed C1q DSA at the time of biopsy in 18 recipients who developed dnDSA. The clinical outcomes of patients with C1q-positive DSA and C1q-negative DSA were compared.
    Results. C1q-positive DSA were detected in 10 of 18 patients (55.6%). The incidences of transplant glomerulopathy were significantly higher among patients with C1q-positive DSA than patients with C1q-negative DSA (80% vs 0%; P ¼ .001). Although patients with C1qpositive DSA experienced more chronic antibody-mediated rejection and graft loss (80% vs 37.5% [P ¼ .145]; 60% vs 25% [P ¼ .188]), the differences were not significant. The receiver operating characteristic curve analysis showed that the C1q assay was an excellent predictor of transplant glomerulopathy with area under the curve of 0.9 (95% CI, 0.769e1.000).
    Conclusion. The presence of C1q-positive dnDSA was associated with an increased risk of transplant glomerulopathy.

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  • Marta Crespo, Alberto Torio, Virginia Mas, Dolores Redondo, Maria J.Pérez-Sáez, Marisa Mir, Anna Faura, Rita Guerra, Olga Montes-Ares, Maria D.Checa, Julio Pascual

    Anti-HLA donor-specific antibodies (DSA) identified by single antigen bead array (SAB) are questioned for their excess in sensitivity and lack of event prediction after transplantation. Population and methods: We retrospectively evaluated specific types of preformed DSA (class I, class II or C1qfixing) and their impact on graft survival. Kidney transplantations performed across negative CDC-crossmatch were included (n = 355). Anti-HLA antibodieswere tested using SAB to identify DSA and their capacity to fix C1q.
    Results: Twenty-eight patients with pretransplant DSA+ with MFI N 2000 were selected to assess C1q fixation. DSA were C1q+in 15 patients and C1q- in 13, without significant differences in demographics, acute rejection, graft loss or renal function. The maximum MFI of DSA in patients with C1q-fixing DSA was significantly higher (p = 0.008). Patients with DSA class-I suffered more antibody-mediated rejection (AMR) and had worse graft survival than class-II. The capacity of DSA I to fix C1q did not correlate with rejection, graft function or graft loss.
    Conclusions: C1q testing in pretransplant serawith DSA was unable to predict acute antibody-mediated rejection or early graft loss, but the presence of DSA class I compared to DSA only class II did. Despite non-fixing complement in vitro, pretransplant C1q-negative DSA I can mediate rejection and graft loss.

    Keywords: Antibody-mediated rejection, Complement, Donor-specific antibody, HLA antibody, Kidney transplantation

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  • Ge Chen and Dolly B. Tyan

    Solid phase Luminex® and flow cytometric single antigen bead assays offer exquisite sensitivity and specifi city for HLA antibody detection. Unlike the historical complement-dependent cytotoxicity (CDC) method, these assays do not distinguish complement fixing from non-complement fixing antibody, the former of which are considered the most clinically relevant in the peri-transplant period. This chapter describes a novel solid phase C1q binding assay to distinguish HLA antibodies that can bind the first component of complement (C1q). These antibodies have the capacity to initiate the complement cascade irrespective of whether that actually occurs. The C1q assay detects many more complement fixing antibodies than are observed by the less sensitive and less specific CDC assay.

    Keywords: HLA antibody, Solid phase assay, Single antigen beads, Luminex®, Transplantation, Complement, C1q

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  • Anat R.Tambur, Jimmy Rosati, Shirley Roitberg, Denis Glotz, John J.Friedewald and Joseph R.Leventhal

    Background. Human leukocyte antigen (HLA)-DQ has emerged as the alloantibody most frequently associated with the generation of de novo donor-specific antibody (DSA), antibody-mediated-rejection, and unfavorable transplantation outcome.
    Methods. The generation of HLA-DQ de novo DSA was interrogated in 40 transplant recipients who were immunologically naive before their failed transplantation. Eplet and epitope analyses were performed using HLAMatchmaker and Cn3D software.
    Results. Ten DQA and thirteen DQB eplets or eplet combinations were identified. All but one revealed an epitope footprint that includes both the DQa and DQb chains. Four examples are illustrated in detail, representing a range of different epitope landscapes. A disparity between antigen density and mean fluorescence intensity values for some alleles within an eplet group was noted, with mean fluorescence intensity values of the lowest fluorescence bead being one tenth of the highest fluorescence bead, despite the fact that the amount of antigen on these beads were not significantly different.
    Conclusion. Our data support the need for changing the manner in which HLA-DQ antigens and antibodies are evaluated for organ transplantation. The current nomenclature system does not reflect the true nature of HLA-DQ polymorphism. Moreover, epitope immunogenicity likely involves more than the mere presence of a specific eplet. Because our field contemplates the use of epitope matching as an approach to improve organ allocation and overall outcomes, it is imperative to have accurate characterization of the immunogenicity of each epitope. This will pave the way to identifying acceptable mismatches and will allow risk stratification for generating de novo HLA-DSA after transplantation.

    Keywords: HLA-DQ, Epitope, HLA-antibody, de novo DSA.

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  • Jeremy M.Blumberg, Hans A.Gritsch, Elaine F.Reed, J.M.Cecka, Gerald S.Lipshutz, Gabriel M.Danovitch, Suzanne McGuire, David W.Gjertson and Jeffrey L.Veale

    Incompatible donor/recipient pairs with broadly sensitized recipients have difficulty finding a crossmatch-compatible match, despite a large kidney paired donation pool. One approach to this problem is to combine kidney paired donation with lower-risk crossmatch-incompatible transplantation with intravenous immunoglobulin. Whether this strategy is non-inferior compared with transplantation of sensitized patients without donor-specific antibody (DSA) is unknown. Here we used a protocol including a virtual crossmatch to identify acceptable crossmatch-incompatible donors and the administration of intravenous immunoglobulin to transplant 12 HLA-sensitized patients (median calculated panel reactive antibody 98%) with allografts from our kidney paired donation program. This group constituted the DSA(þ) kidney paired donation group. We compared rates of rejection and survival between the DSA(þ) kidney paired donation group with a similar group of 10 highly sensitized patients (median calculated panel reactive antibody 85%) that underwent DSA() kidney paired donation transplantation without intravenous immunoglobulin. At median follow-up of 22 months, the DSA(þ) kidney paired donation group had patient and graft survival of 100%. Three patients in the DSA(þ) kidney paired donation group experienced antibody-mediated rejection. Patient and graft survival in the DSA() kidney paired donation recipients was 100% at median follow-up of 18 months. No rejection occurred in the DSA() kidney paired donation group. Thus, our study provides a clinical framework through which kidney paired donation can be performed with acceptable outcomes across a crossmatch-incompatible transplant.

    Keywords: desensitization; donor-specific HLA antibodies; kidney paired donation; living-donor kidney transplantation

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  • Immunoassays announcement on ASHI site

    IMMUNOASSAYS WEBSITE

    In response to discussions at the 16th International Histocompatibility and Immunogenetics Workshop, members of the Johns Hopkins Immunogenetics Laboratory have created a website for all things related to solid phase antibody immunoassays.  At www.immunoassays.net, you can enter into discussions about test interpretation and troubleshooting. The site provides information on the latest assays, performance of different test lots, correlations between solid phase and cell based test results, and serum treatments.  There is information on bead assays, flow cytometry and ELISA as well as links to relevant publications. Please visit the website and become a member at www.immunoassays.net.  You can become a site moderator and lead discussions.  

    Source: Ashi-hla.org

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  • B.J.Orandi, J.M.Garonzik-Wang, A.B.Massie, A.A.Zachary, J.R.Montgomery, K.J.Van Arendonk, M.D.Stegall, S.C.Jordan, J.Oberholzer, T.B.Dunn, L.E.Ratner, S.Kapur, R.P.Pelletier, J.P.Roberts, M.L.Melcher, P.Singh, D.L.Sudan, M.P.Posner, J.M.El-Amm, R.Shapiro, M.Cooper, G.S.Lipkowitz, M.A.Rees, C.L.Marsh, B.R.Sankari, D.A.Gerber, P.W.Nelson, J.Wellen, A.Bozorgzadeh, A.O.Gaber, R.A.Montgomery and D.L.Segev

    Incompatible live donor kidney transplantation (ILDKT) offers a survival advantage over dialysis to patients with anti-HLA donor-specific antibody (DSA). Programspecific reports (PSRs) fail to account for ILDKT, placing this practice at regulatory risk. We collected DSA data, categorized as positive Luminex, negative flow crossmatch (PLNF) (n¼185), positive flow, negative cytotoxic crossmatch (PFNC) (n¼536) or positive cytotoxic crossmatch (PCC) (n¼304), from 22 centers. We tested associations between DSA, graft loss and mortality after adjusting for PSR model factors, using 9669 compatible patients as a comparison. PLNF patients had similar graft loss; however, PFNC (adjusted hazard ratio [aHR]¼1.64, 95% confidence interval [CI]: 1.15–2.23, p¼0.007) and PCC (aHR¼5.01, 95% CI: 3.71–6.77, p<0.001) were associated with increased graft loss in the first year. PLNF patients had similar mortality; however, PFNC (aHR¼2.04; 95% CI: 1.28–3.26; p¼0.003) and PCC (aHR¼4.59; 95% CI: 2.98–7.07; p<0.001) were associated with increased mortality. We simulated Centers for Medicare & Medicaid Services flagging to examine ILDKT’s effect on the risk of being flagged. Compared to equal-quality centers performing no ILDKT, centers performing 5%, 10% or 20% PFNC had a 1.19-, 1.33- and 1.73-fold higher odds of being flagged. Centers performing 5%, 10% or 20% PCC had a 2.22-, 4.09- and 10.72-fold higher odds. Failure to account for ILDKT’s increased risk places centers providing this life-saving treatment in jeopardy of regulatory intervention.

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  • J.G.O’Leary, A.J.Demetris, L.S.Friedman, H.M.Gebel, P.F.Halloran, A.D.Kirk, S.J.Knechtle, S.V.McDiarmid, A.Shaked, P.I.Terasaki, K.J.Tinckam, S.J.Tomlanovich, K.J.Wood, E.S.Woodle, A.A.Zachary and G.B.Klintmalm

    Several insights emerged. Acute antibody-mediated rejection (AMR), although rarely diagnosed, is increasingly understood to overlap with T cell–mediated rejection. Isolated liver allograft recipients are at increased risk of early allograft immunologic injury when preformed DSA are high titer and persist posttransplantation. Persons who undergo simultaneous liver–kidney transplantation are at risk of renal AMR when Class II DSA persist posttransplantation. Other under-appreciated DSA associations include ductopenia and fibrosis, plasma cell hepatitis, biliary strictures and accelerated fibrosis associated with recurrent liver disease. Standardized DSA testing and diagnostic criteria for both acute and chronic AMR are needed to distil existing associations into etiological processes in order to develop responsive therapeutic strategies.

    Keywords: Antibody-mediated rejection, donor-specific HLA antibodies, graft outcomes, liver transplant, renal transplant, simultaneous liver–kidney transplant.

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  • Brian D.Tait, Caner Susal, Howard M.Gebel, Peter W.Nickerson, Andrea A.Zachary, Frans H.J.Claas, Elaine F.Reed, Robert A.Bray, Patricia Campbell, Jeremy R.Chapman, P.Toby Coates, Robert B.Colvin, Emanuele Cozzi, Ilias I.N.Doxiadis, Susan V.Fuggle, John Gill, Denis Glotz, Nils Lachmann, Thalachallour Mohanakumar, Nicole Suciu-Foca, Suchitra Sumitran-Holgersson, Kazunari Tanabe, Craig J.Taylor, Dolly B.Tyan, Angela Webster, Adriana Zeevi, and Gerhard Opelz

    Background. The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results.
    Methods. With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a ‘‘Consensus Conference on Antibodies in Transplantation’’ in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report.
    Results. A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if singleantigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results.
    Conclusions. A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

    Keywords: Transplantation, HLA, Antibodies.

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  • Andrea A. Zachary, Mary S. Leffell

    Summary: Desensitization protocols are being used worldwide to enable kidney transplantation across immunologic barriers, i.e. antibody to donor HLA or ABO antigens, which were once thought to be absolute
    contraindications to transplantation. Desensitization protocols are also being applied to permit transplantation of HLA mismatched hematopoietic stem cells to patients with antibody to donor HLA, to enhance the opportunity for transplantation of non-renal organs, and to treat antibody-mediated rejection. Although desensitization for organ transplantation carries an increased risk of antibody-mediated rejection, ultimately these transplants extend and enhance the quality of life for solid organ recipients, and desensitization that permits transplantation of hematopoietic stem cells is life saving for patients with limited donor options. Complex patient factors and variability in treatment protocols have made it difficult to identify, precisely, the mechanisms underlying the downregulation of donor-specific antibodies. The mechanisms underlying desensitization may differ among the various protocols in use, although there are likely to be some common features. However, it is likely that desensitization achieves a sort of immune detente by first reducing the immunologic barrier and then by creating an environment in which an autoregulatory process restricts the immune response to the allograft.

    Keywords: desensitization, donor-specific antibodies, solid organ transplantation, hematopoietic stem cell transplantation, plasmapheresis, intravenous immunoglobulin

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  • Annette M. Jackson, Mary S. Leffell, Robert A. Montgomery, and Andrea A. Zachary

    Purpose of review
    To identify factors that affect the choice of route to renal transplantation for the sensitized patient. The evolution of protocols for transplanting sensitized patients has been desensitization (DES), paired donation, and most recently, paired donation combined with DES. Use of these protocols has revealed various factors that influence which route is the most likely to work for a given patient.
    Recent findings
    The data indicate that patient blood type and HLA sensitization have the dominant influence on what route is best for a patient but numerous other factors, particularly the number, HLA type, and ABO type of donors a patient brings to a program will also affect the likelihood of transplantation. The distribution of these factors among patients transplanted or unable to find a compatible donor can be used to calculate the probability of transplantation via paired donation.
    Summary
    Kidney paired donation with or without DES provides benefits that cannot be achieved with DES alone. However, DES may provide the fastest route to transplantation.

    Keywords: desensitization, HLA antibodies, kidney paired donation, 

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  • Robert A. Montgomery, Bonnie E. Lonze and Annette M. Jackson

    Purpose of review
    Many sensitized patients have willing live donors but are unable to use them because of a human leukocyte antigen (HLA) incompatibility. The options for these patients include: remaining on the deceased-donor list, entering a kidney-paired donation scheme, or undergoing desensitization with high-dose IVIg or plasmapheresis and low-dose IVIg.
    Recent findings
    Mathematical simulations verified by actual data from several national kidney-paired donation (KPD) programs has shed light on which donor/recipient phenotypes are likely to benefit from each transplant modality. Pairs that are easy to match are likely to receive compatible kidneys in a KPD. Those who are hard to match may be better served by desensitization. The phenotype which is both hard to match and hard to desensitize due to board and strong HLA reactivity are most likely to be transplanted by a hybrid modality utilizing desensitization after identifying a more immunologically favorable donor in a KPD.
    Summary
    Recent outcomes from desensitization in which starting donor-specific antibody strength is low have been very good. For broadly sensitized patients with a high-strength cross-match, searching for a better donor in a KPD pool can facilitate a safer, less expensive, and more successful desensitization treatment course.

    Keywords: desensitization, highly sensitized, kidney exchanges, kidney-paired donation, plasmapheresis

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  • Annette M. Jackson, Edward S. Kraus, Babak J. Orandi, Dorry L. Segev, Robert A. Montgomery and Andrea A. Zachary

    Rituximab has been used to increase the efficacy of desensitization protocols for human leukocyte antigen (HLA)-incompatible kidney transplantation; however, controlled comparisons have not been reported. Here we examined 256 post-transplant HLA antibody levels in 25 recipients desensitized with and 25 without rituximab induction, to determine the impact of B-cell depletion. We found significantly less HLA antibody rebound in the rituximab-treated patients (7% of donor-specific antibodies (DSAs) and 33% of non-DSAs) compared with a control cohort desensitized and transplanted without rituximab (32%
    DSAs and 55% non-DSAs). The magnitude of the increase was significantly larger among patients who did not receive rituximab. Interestingly, in rituximab-treated patients, of the 39 HLA antibodies that increased post transplant, 34 were specific for HLA mismatches present in previous allografts or pregnancies, implying limited efficacy in memory B-cell depletion. Compared with controls, rituximab-treated
    patients had a significantly greater mean reduction in DSA (2505 vs. 292 mean fluorescence intensity), but a similar rate of DSA persistence (52% in rituximab treated-and 40% in non-treated recipients). Thus, rituximab induction in HLA-incompatible recipients reduced the incidence and magnitude of HLA antibody rebound, but did not affect DSA elimination, antibody-mediated rejection, or 5-year allograft
    survival when compared with recipients desensitized and transplanted without rituximab.

    Keywords: B cells; desensitization; HLA antibody; kidney transplantation; rituximab

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  • Mary Carmelle Philogene, Paul Sikorski, Robert A. Montgomery, Mary S. Leffell, and Andrea A. Zachary

    Background. Bortezomib has been used to reduce HLA antibody in patients either before transplantation or as treatment
    for antibody-mediated rejection (AMR). Reports on its efficacy show mixed results. The mechanism of action
    of this agent is via proteasome inhibition. The primary route of synthesis of HLA class I molecules is dependent on
    peptide generation by the proteasome, whereas that of class II is not. We observed a differential effect of bortezomib on
    class I versus class II antibody and hypothesized that this was related to a reduced expression of class I HLA antigens.
    Methods. The effect of bortezomib on HLA antibody levels was evaluated in 13 patients who were desensitized for
    incompatible renal transplantation. We calculated the percent difference in HLA antibody level before and after bortezomib
    treatment and the impact of bortezomib on HLA expression in lymphocytes of healthy control subjects.
    Results. On average, the level of HLA class I donor-specific antibody (DSA) decreased by 32%, whereas that of class II
    DSA increased by 29%. In vitro bortezomib treatment of lymphocytes resulted in a mean decrease of 23% in MHC
    class I expression on B lymphocytes and no change (+1.08%) in MHC class II expression (P=0.0003). The amount
    of intracellular class I molecules was reduced by a mean of 29% with bortezomib.
    Conclusion. These data indicate that bortezomib reduces HLA class I antibody more effectively than class II antibody.
    This difference may be due to the reduced expression of class I molecules resulting from treatment with this proteasome
    inhibitor.

    Keywords: Bortezomib, HLA antibody, Renal transplantation, Proteasome inhibition, MHC molecules.

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