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Access to kidney transplantation is limited by HLA-specific sensitization. Desensitization strategies enable crossmatch-positive kidney transplantation. In this review, we describe clinical experience gained over the last 20 y using desensitization strategies before kidney transplantation and describe the different tools used (both drugs and apheresis options), including IVIg, rituximab, apheresis techniques, interleukin-6 interference, proteasome inhibition, enzymatic degradation of HLA antibodies, complement inhibition, and B cytokine interference. Although access to transplantation for highly sensitized kidney transplantation candidates has been vastly improved by desensitization strategies, it remains, however, limited by the recurrence of HLA antibodies after transplantation and the occurrence of antibody-mediated rejection., Competing Interests: L.R. has received honoraria from BMS and Hansa Bopharma. The other authors declare no conflicts of interest., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Resistance to the action of rituximab (RTX) has been documented in several diseases. More recently, obinutuzumab (OBZ) has shown promise where RTX has failed in oncology and lupus nephritis. Unlike RTX, OBZ is a weak activator of complement, which may avoid the false-positive complement-dependent cytotoxicity (CDC) crossmatch tests after RTX infusions., Methods: The aim of this study was to explore the effect of OBZ on B-cell depletion in kidney-transplant candidates and its impact on crossmatch test results. We included 12 patients, who were either highly sensitized kidney-transplant candidates or kidney-transplant recipients presenting with antibody-mediated rejection. Six received OBZ, and 6 received RTX. CD-19 counts, flow cytometry, and CDC crossmatch tests were run immediately before and at 2 wk after drug infusion., Results: OBZ reduced CD-19 counts: median reduction was 98%. B-cell CDC crossmatch test results became positive following RTX infusion but were not affected by OBZ infusion., Conclusions: OBZ effectively depleted B-cell counts in sensitized kidney-transplant candidates and, unlike RTX, had no effect on CDC crossmatch results., Competing Interests: The authors declare no funding or conflicts of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Background: The impact of donor-specific anti-HLA antibodies (DSA) on antibody-mediated rejection (AMR) and kidney allograft failure is well established. However, the relevance of non-HLA antibodies remains unclear., Methods: We investigated 13 pretransplant non-HLA antibodies and their association with histology of AMR (AMRh) and kidney allograft failure. We included single kidney recipients (n = 203) with AMRh, according to the Banff 2017 classification and matched AMRh-free controls (n = 219). Non-HLA antibodies were assessed using multiplex Luminex assay., Results: Of the selected non-HLA antibodies (against agrin, adipocyte plasma membrane-associated protein, Rho GDP-dissociation inhibitor 2 [ARHGDIB], Rho guanine nucleotide exchange factor 6, angiotensin-II type 1 receptor, endothelin type A receptor, lamin B1, BPI fold-containing family B member 1, peroxisomal trans-2-enoyl-coenzyme A reductase, phospholipase A2 receptor, protein kinase C zeta type, tubulin beta-4B class IVb, vimentin), only antibodies against ARHGDIB (adjusted median fluorescence intensity [aMFI] ≥ 1000), a minor histocompatibility antigen, associated with graft failure, in univariate and multivariate models (hazard ratio = 2.7; 95% confidence interval [CI],1.3-5.4; P = 0.007). There was a 19.5-fold (95% CI, 6.0-63.9; P < 0.0001) increased risk of graft failure in patients positive for both DSA and anti-ARHGDIB antibodies (aMFI ≥ 1000) versus patients negative for both DSA and anti-ARHGDIB antibodies, compared with a 4.4-fold (95% CI, 2.4-8.2; P < 0.0001) increased risk in patients with only DSA, and a 4.1-fold (95% CI, 1.4-11.7; P = 0.009) increased risk in patients with only anti-ARHGDIB antibodies above 2000 aMFI. AMRh associated with increased intrarenal expression of the ARHGDIB gene. In the absence of AMRh and DSA, anti-ARHGDIB antibodies were not clearly associated with graft failure., Conclusions: The presence of pretransplant anti-ARHGDIB antibodies has an additive effect in patients with DSA on the risk of graft failure via AMRh. Other investigated non-HLA antibodies, including antibodies against angiotensin-II type 1 receptor, did not contribute to risk stratification and could not explain the histology of AMR in the absence of DSA.

Background: It is estimated that 19.2% of kidneys exported for candidates with >98% calculated panel reactive antibodies are transplanted into unintended recipients, most commonly due to positive physical crossmatch (PXM). We describe the application of a virtual crossmatch (VXM) that has resulted in a very low rate of transplantation into unintended recipients., Methods: We performed a retrospective review of kidneys imported to our center to assess the reasons driving late reallocation based on the type of pretransplant crossmatch used for the intended recipient., Results: From December 2014 to October 2017, 254 kidneys were imported based on our assessment of a VXM. Of these, 215 (84.6%) were transplanted without a pretransplant PXM. The remaining 39 (15.4%) recipients required a PXM on admission using a new sample because they did not have an HLA antibody test within the preceding 3 months or because they had a recent blood transfusion. A total of 93% of the imported kidneys were transplanted into intended recipients. There were 18 late reallocations: 9 (3.5%) due to identification of a new recipient medical problem upon admission, 5 (2%) due to suboptimal organ quality on arrival, and only 4 (1.6%) due to a positive PXM or HLA antibody concern. A total of 42% of the recipients of imported kidneys had a 100% calculated panel reactive antibodies. There were no hyperacute rejections and very infrequent acute rejection in the first year suggesting no evidence for immunologic memory response., Conclusions: Seamless sharing is within reach, even when kidneys are shipped long distances for highly sensitized recipients. Late reallocations can be almost entirely avoided with a strategy that relies heavily on VXM.

Background: HLA-specific memory B cells may contribute to the serum HLA antibody pool upon antigen reexposure. The aim of this pilot study was to investigate the presence of concurrent donor-specific memory B cell-derived HLA antibodies (DSA-M) in renal allograft recipients with pretransplant donor-specific HLA antibodies (DSA) and its association with occurrence of antibody-mediated rejection (AMR) using a recently developed method., Methods: Twenty patients with Luminex single antigen bead (SAB) assay-defined DSA but negative complement-dependent cytotoxicity crossmatches were enrolled. Plasma samples and peripheral blood mononuclear cells were collected at 3 timepoints (pretransplant, mo 6, mo 12). We analyzed IgG-purified and concentrated culture supernatants from polyclonally activated peripheral blood mononuclear cells using SAB assays and compared HLA antibody profiles with same day plasma results., Results: Plasma SAB analysis revealed 35 DSA in 20 patients pretransplant. DSA-M were detected in 9 of 20 (45%) patients and for 10 of 35 specificities (29%). While median mean fluorescence intensity values of DSA with concurrent DSA-M (5877) were higher than those of DSA without DSA-M (1476), 3 of 6 patients with AMR and low mean fluorescence intensity DSA (<3000) had DSA-M. Overall, pretransplant DSA/DSA-Mpos allograft recipients showed a higher incidence of biopsy-proven (sub)clinical AMR (P = 0.032) and a higher extent (g≥1 + ptc≥1) of microvascular inflammation (67% vs 9%, P = 0.02). In 17 patients (28 DSA) with posttransplant analyses, persisting DSA posttransplant had more often DSA-M (6/12; 50%) than nonpersisting DSA (2/16; 13%)., Conclusions: Assessment of DSA-M might be a novel tool to supplement serum HLA antibody analysis for pretransplant risk stratification in patients with DSA.

Background: While tacrolimus and sirolimus (T/S)-based graft-versus-host disease (GvHD) prophylaxis has been effective in preventing acute GvHD post hematopoietic cell transplantation (HCT), its efficacy and long-term outcome in matched (MUD) and mismatched unrelated donor (mMUD) setting is not well defined., Methods: Herein, we evaluated a consecutive case-series of 482 patients who underwent unrelated donor HCT (2005-2013) with T/S-based GvHD prophylaxis., Results: With a median follow-up of 6.2 years (range = 2.4-11.3), the 5-year overall survival (OS) and relapse/progression-free survival were 47.5% (95% confidence interval [CI]: 43.0-52.0) and 43.6% (95% CI: 39.1-48.1), respectively; and the 5-year cumulative incidence of nonrelapse mortality (NRM) and relapse were 24.9%, and 31.5%, respectively. In this cohort, mMUD was associated with worse OS (39.0% versus 50.7% at 5 y; P = 0.034), primarily due to greater risk of NRM (33.5% versus 21.7%; P = 0.038). While rates of relapse, acute (II-IV or III-IV) or chronic GvHD (limited or extensive) were not different, death caused by chronic GvHD (20.8% versus 12.8%; P = 0.022) and infection (33.0% versus 18.1%; P < 0.01) were significantly greater in mMUD. In multivariable analysis, high-risk disease (hazard ratio [HR] = 2.21, 95% CI: 1.16-4.23; P < 0.01) and mMUD (HR = 1.55, 95% CI: 1.15-2.08; P = 0.004) were independent predictive factors for OS., Conclusions: T/S-based GvHD prophylaxis is an effective and acceptable GvHD prophylactic regimen. However, survival after mMUD remained poor, possibly related to the severity of chronic GvHD.

Background: Donor-specific HLA antibodies (DSA) are associated with increased rates of rejection and of graft failure in cardiac transplantation. The goal of this study was to determine the association of preformed and posttransplant development of newly detected DSA (ndDSA) with antibody-mediated rejection (AMR) and characterize the clinical relevance of complement-activating DSA in heart allograft recipients., Methods: The study included 128 adult and 48 pediatric heart transplant patients transplanted between 2010 and 2013. Routine posttransplant HLA antibody testing was performed by IgG single-antigen bead test. The C3d single-antigen bead assay was used to identify complement-activating antibodies. Rejection was diagnosed using International Society for Heart and Lung Transplantation criteria., Results: In this study, 22 patients were transplanted with preexisting DSA, and 43 patients developed ndDSA posttransplant. Pretransplant (P < 0.05) and posttransplant (P < 0.001) ndDSA were associated with higher incidence of AMR. Patients with C3d + DSA had significantly higher incidence of AMR compared with patients with no DSA (P < 0.001) or patients with C3d-DSA (P = 0.02). Nine (36%) of 25 patients with AMR developed transplant coronary artery disease compared with 17 (15.9%) of 107 patients without AMR (P < 0.05). Among the 47 patients who received ventricular assistant device (VAD), 7 of 9 VAD+ patients with preformed DSA experienced AMR compared with 7 of 38 VAD+ patients without preformed DSA, indicating presensitization to donor HLA significantly increased the risk of AMR (P < 0.01)., Conclusions: Preformed and posttransplant ndDSA were associated with AMR. C3d + DSA correlates with complement deposition on the graft and higher risk of AMR which may permit the application of personalized immunotherapy targeting the complement pathway.

The evolution of antibody detection from cell- to bead-based technology has positively impacted the ability to allocate organs in a safe and timely manner. The devil, of course, is in the details that delineate how these assays are performed and applied and to recognize that while there have been some truly amazing technological advances (assets), they are still imperfect and subject to error (liabilities). This review identifies the strengths of HLA antibody assays, highlights their weaknesses and offers approaches for standardization.

HLA antibodies, and specifically donor-specific-HLA antibodies, play a key role in transplant-related diagnostics and decision-making. It is now clear that the simple differentiation between absence and presence of HLA donor-specific antibodies does not provide sufficient granularity in all clinical circumstances. It addition, knowledge of HLA antibody strength has potential utility at different stages of recipient evaluation along the transplant timeline from initial pretransplant evaluation, evaluation of a specific potential donor, and posttransplant monitoring for de novo donor-specific antibodies. Here we compare data evaluating HLA antibody strength using the conventional IgG-mean fluorescence intensity approach with serial dilution studies (titration) and of C1q binding (C1q-mean fluorescence intensity). The added value of titration studies along the 3 milestones of the transplant cycle is emphasized.

Formation of antibodies against polymorphic HLA molecules on donor endothelium is central to the pathogenesis of antibody-mediated rejection, the dominant cause of long-term kidney allograft loss. Although introduction of the single-antigen bead assay has greatly facilitated the immune risk assessment of transplant recipients, it is recognized that not all IgG HLA antibodies detected using this method are equally relevant. In recent years, novel assays (C4d, C1q, C3d) have been developed to interrogate the complement-activating potential of anti-HLA antibodies in vitro, with the hypothesis that complement-fixing antibodies are more immediately injurious to the graft compared with noncomplement-binding antibodies. Although initial studies demonstrated the potential of these assays to risk-stratify antibodies beyond the conventional limited metric of mean fluorescence intensity values, new data from recent analyses challenge some of these early findings. In this review, we examine the technical aspects of these assays and key studies that evaluated the discriminant capacity of these tests to predict numerous outcomes in kidney transplantation. We discuss conflicting data and emerging controversies in the context of recent experimental evidence which offer new insights into the major factors that influence complement activation. Finally, we provide our perspective on the current role and utility of complement diagnostic assays as 1 variable in the multifactorial risk assessment and management of kidney transplant recipients.

This overview describes recent developments demonstrating the significance of epitopes in HLA antibody responses and matching for organ transplantation. HLA epitopes are defined by molecular modeling and amino acid comparisons between HLA alleles and the HLAMatchmaker algorithm considers eplets as essential components. Each allele represents a distinct string of eplets and matching is done by aligning donor and recipient strings. Evidence is summarized how mismatched eplet loads affect antibody responses and transplant outcomes. Epitope-based matching has been applied not only to identify acceptable mismatches for sensitized transplant candidates but also to identify more suitably mismatched donors for nonsensitized patients. Three recently proposed theories will further our understanding of the immunogenicity of individual HLA eplets.It has become apparent that epitope-based matching is superior to antigen matching; we should be ready soon to apply this principle in the clinical transplant setting very soon.

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 high-level 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 = 0.42). ethylene diamine tetraacetic acid and serum dilution improved the correlation (r = 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 (r = 0.40) and highest using diluted sera and SAB with 30% or less denatured HLA (r = 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.

Background: The presence of antibodies to angiotensin type 1 receptor (AT1R) and endothelin type A receptor (ETAR) is associated with allograft rejection in kidney and heart transplantation. The aim of our study was to determine the impact of AT1R and ETAR antibodies on graft outcome in lung transplantation., Methods: Pretransplant and posttransplant sera from 162 lung recipients transplanted at 3 centers between 2011 and 2013 were tested for antibodies to AT1R and ETAR by the enzyme-linked immunosorbent assay (ELISA) assay. Clinical parameters analyzed were: HLA antibodies at transplant, de novo donor-specific antibodies (DSA), antibody-mediated rejection (AMR), acute cellular rejection, and graft status., Results: Late AMR (median posttransplant day 323) was diagnosed in 5 of 36 recipients with de novo DSA. Freedom from AMR significantly decreased for those recipients with strong/intermediate binding antibodies to AT1R (P = 0.014) and ETAR (P = 0.005). Trends for lower freedom from acute cellular rejection were observed for recipients with pretransplant antibodies to AT1R (P = 0.19) and ETAR (P = 0.32), but did not reach statistical significance. Lower freedom from the development of de novo DSA was observed for recipients with antibodies detected pretransplant to AT1R (P = 0.054), ETAR (P = 0.012), and HLA-specific antibodies (P = 0.063). When the pretransplant antibody status of HLA-specific antibody (hazard ratio [HR], 1.69) was considered together with either strong binding to AT1R or ETAR, an increased negative impact on the freedom from the development of de novo DSA was observed (HR, 2.26 for HLA antibodies and ETAR; HR, 2.38 for HLA antibodies and ETAR)., Conclusions: These results illustrate the increased negative impact when antibodies to both HLA and non-HLA antigens are present pretransplant.

Background: Antipig antibodies are a barrier to clinical xenotransplantation. We evaluated antibody binding of waitlisted renal transplant patients to 3 glycan knockout (KO) pig cells and class I swine leukocyte antigens (SLA)., Methods: Peripheral blood mononuclear cells from SLA identical wild type (WT), α1, 3-galactosyltransferase (GGTA1) KO, GGTA1/ cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) KO, and GGTA1/ CMAH /b1,4 N-acetylgalactosaminyl transferase (B4GalNT2) KO pigs were screened for human antibody binding using flow cytometric crossmatch (FCXM). Sera from 820 patients were screened on GGTA1/CMAH/B4GalNT2 KO cells and a subset with elevated binding was evaluated further. FCXM was performed on SLA intact cells and GGTA1/SLA class I KO cells after depletion with WT pig RBCs to remove cell surface reactive antibodies, but leave SLA antibodies. Lastly, human and pig reactive antibodies were eluted and tested for cross-species binding and reactivity to single-antigen HLA beads., Results: Sequential glycan KO modifications significantly reduce antibody binding of waitlisted patients. Sera exhibiting elevated binding without reduction after depletion with WT RBCs demonstrate reduced binding to SLA class I KO cells. Human IgG, eluted from human and pig peripheral blood mononuclear cells, interacted across species and bound single-antigen HLA beads in common epitope-restricted patterns., Conclusions: Many waitlisted patients have minimal xenoreactive antibody binding to the triple KO pig, but some HLA antibodies in sensitized patients cross-react with class I SLA. SLA class I is a target for genome editing in xenotransplantation.

Background: Single antigen beads (SAB) are used for monitoring HLA antibodies in pretransplant and posttransplant patients despite the discrepancy between virtual and actual crossmatch results and transplant outcomes. This discrepancy can be attributed to the presence of conformational variants of HLA-I on SAB, assessment of which would increase the concordance between SAB and flow cytometry crossmatch (FCXM) results, thus enabling improved organ accessibility for the waiting list patients and a better prediction of antibody-mediated rejection., Methods: The conformational variants were examined on HLA-I beads, iBeads, acid-/alkali-treated beads, and T cells using HLA-I monoclonal antibodies (W6/32, TFL-006, and heavy chain (HC)-10)., Results: The affinity of the monoclonal antibodies against HLA-I beads confirmed the presence and heterogeneous density of peptide-associated β2-microglobulin-associated HLA HC (pepA-β2aHC), peptide-free-β2aHC (pepF-β2aHC), and β2-free HC (β2fHC) on every single antigen-coated bead. In contrast, iBeads harbor a high density of pepA-β2aHC, low density of pepF-β2aHC, and are lacking β2fHC. The FCXM analyses confirmed the prevalence of pepA-β2aHC, but not pepF-β2aHC or β2fHC on resting T cells., Conclusions: The strength of a donor-specific antibody should be assessed with a bead-specific mean fluorescence intensity cutoff based on TFL-006 reactivity against HLA-I beads, and HC-10 against iBeads, where the β2fHC or pepF-β2aHC normalized donor-specific antibody level would reveal the true anti-pepA-β2aHC reactivity associated with positive FCXM.

Background: Participation of compatible pairs (CP) in kidney paired donation (KPD) could be attractive to CPs who have a high degree of HLA mismatch, if the CP recipient will gain a better HLA match. Because KPD programs were not designed to help CP, it is important to define allocation metrics that enable CP to receive a better-matched kidney, without disadvantage to incompatible pairs (ICP)., Methods: Simulations using 46 ICPs and 11 fully HLA-mismatched CPs were undertaken using the Australian KPD matching algorithm. Allocations were preformed adding 1 CP at a time or all 11 CPs at once, and with and without exclusion of unacceptable antigens selected to give a virtual calculated panel-reactive antibody ranging 70% to 80% to improve HLA matching in CP recipients., Results: On average, most CP recipients could be matched and had a lower eplet mismatch (EpMM) with the matched donor (57 ± 15) than with their own donor (78 ± 19, P < 0.02). However, only recipients who had an EpMM to own donor greater than 65 achieved a significant reduction in the EpMM with the matched donor. The gain in EpMM was larger when CPs were listed with unacceptable antigens. Furthermore, inclusion of 1 CP at a time increased matching in ICP by up to 33%, and inclusion of all 11 CPs at once increased ICP matching by 50%., Conclusions: Compatible pair participation in KPD can increase match rates in ICP and can provide a better immunological profile in CP recipients who have a high EpMM to their own donor when using allocation based on virtual crossmatch.

Background: In virtual crossmatch (XM) strategies, a correct anticipation of XM results is required for appropriately allocating organs. We reassessed the ability to predict T lymphocyte flow cytometry and complement dependent cytotoxicity XM results with the mean fluorescence intensity (MFI) in Luminex class I single antigen flow beads (SAFB) assay, after correction of complement interference and exclusion of antidenatured HLA antibodies., Methods: Among 432 XM with T lymphocytes (T-XM), 407 were analyzed after exclusion of antidenatured HLA antibodies. Only ethylenediaminetetraacetic acid-treated serum MFI was considered. Only 1 cellular target HLA antigen for the serum was expressed in 238 cases, 209 and 29 being heterozygous and homozygous for this antigen, respectively. For the remaining 169 cases, at least 2 antigens were recognized. Single antigen flow bead MFI thresholds allowing XM positivity to be predicted were calculated with receiver operating characteristic curves., Results: T-XM results were tightly associated with SAFB MFI values. Anti-HLA-A and anti-HLA-B antibodies behaved similarly. Prediction and sensitivity SAFB MFI thresholds were determined, respectively, assessing the highest sensitivity/specificity ratio and at least 95% sensitivity for predicting T-XM positivity. Both were slightly lower for HLA-B than for HLA-A, whereas anti-HLA-Cw antibodies induced random XM results. Both thresholds were only slightly diminished for homozygous and for multiple HLA targets, considering the immunodominant, but not the sum, of antibodies MFI., Conclusions: Antibodies against HLA-A, -B, or -Cw behave differently. A homozygous HLA target does not trigger a twice higher XM positivity. Multiple antibodies are better evaluated through the immunodominant DSA MFI than through the sum of DSA MFI.

Alloreactive T lymphocytes are the primary mediators of allograft rejection. The size and diversity of the HLA-alloreactive T cell repertoire has thus far precluded the ability to follow these T cells and thereby to understand their fate in human transplant recipients. This review summarizes the history, challenges, and recent advances in the study of alloreactive T cells. We highlight the historical development of assays to measure alloreactivity and discuss how high-throughput T cell receptor (TCR) sequencing-based assays can provide a new window into the fate of alloreactive T cells in human transplant recipients. A specific approach combining a classical in vitro assay, the mixed lymphocyte reaction, with deep T cell receptor sequencing is described as a tool to track the donor-reactive T cell repertoire for any specific HLA-mismatched donor-recipient pair. This assay can provide mechanistic insights and has potential as a noninvasive, highly specific biomarker for rejection and tolerance.

The development of sensitive methods for alloantibody detection has been a significant advance in clinical transplantation. However, the complexity of the data from solid phase and crossmatch assays has led to potential confusion about how to use the results for clinical decision making. The goal of this review is to provide a practical guide for transplant physicians for the interpretation of antibody data to supplement consultation with local tissue typing experts. Sources of variability in both the solid phase and crossmatch assay are discussed as are recent data regarding C1q binding antibodies and IgG subclass testing. Although definitive approaches to alloantibody testing are not possible with our current knowledge, we outline a pragmatic approach that we hope will enhance clinical management in this area.

Background: The association of donor-specific HLA antibodies (DSA) with kidney graft failure has been addressed previously; however, the majority of studies were based on small numbers of patients with graft failure., Methods: We investigated 83 patients with failed kidney transplants for a possible association of de novo development and persistence or loss of pre-existing DSA with graft failure. Single Antigen Bead assay-detected DSA and non-DSA antibodies were compared between patients with graft loss and matched controls with functioning grafts., Results: The incidence of weak de novo DSA or non-DSA at a mean fluorescence intensity of 500 or higher was higher in the graft loss than in the nonrejector group (76% vs 40%, P < 0.001). Because of the low number of patients developing de novo DSA, the DSA results did not reach statistical significance (only 22% of patients with graft loss developed de novo DSA). However, at all cutoffs, there was a significantly higher rate of graft loss in patients with de novo non-DSA. The incidence of strong pretransplant DSA that persist after transplantation was higher in the graft loss group (10% vs 1%, P = 0.034). When C1q-binding ability in sera of rejectors and nonrejectors with posttransplant de novo or persistent DSA was compared, none of the nonrejectors demonstrated C1q positivity, whereas 43% of patients with graft loss showed C1q-positive antibodies, although not necessarily donor-specific (P < 0.001)., Conclusions: Our data show that the posttransplant presence of persisting or de novo HLA antibodies, especially if C1q binding, is associated with graft loss, even if the antibodies are not specific for mismatched donor HLA.

Background: Single antigen flow beads assays may overestimate sensitization because of the detection of supposedly irrelevant antibodies recognizing denatured class I human leukocyte antigens (HLAs)., Methods: Sera of 323 HLA-sensitized kidney transplant candidates positive with a class I HLA single antigen flow beads assay were retested after acid treatment of the beads. Denatured HLA antibodies were identified according to ratio between the measured fluorescence intensity for treated and nontreated beads. T-lymphocyte flow cytometry crossmatches were performed to characterize the ability of these antibodies to recognize HLA on normal cells as a surrogate of their potential clinical relevance. Their impact on organ allocation was evaluated through a calculated panel reactive antibody. The utility of single antigen flow beads largely devoid of denatured HLA (iBeads) was also evaluated., Results: Denatured HLA antibodies were detected in 39% of the patients. They provided much less positive flow cytometry crossmatches than anti-native HLA antibodies (16% vs. 83%, P<0.0001). Removing the HLA-A and HLA-B antigens targeted by denatured HLA antibodies from unacceptable antigens lowered the calculated panel reactive antibody for 90 patients, sometimes dramatically. The iBeads assay demonstrated nearly the same ability to predict crossmatch results than the acid treatment assay., Conclusion: Denatured class I HLA antibodies are common, but the antigens they target should not be considered as unacceptable in most cases, because they negatively impact access to a transplant while predominantly providing negative sensitive crossmatches. The iBeads assay seems to be a valuable alternative to better define unacceptable antigens.

Background: Luminex-based anti-HLA IgG detection on single-antigen flow beads (SAFB) represents a valuable tool for characterization of allosensitization patterns. Assay interpretation, however, may be impeded by false-low test results caused by the prozone effect. Recent experimental data have related this artifact to direct blockade of IgG detection by complement component C1 as a possible candidate mechanism., Methods: To dissect a causative role of C1 complex formation and subsequent steps of classical complement activation, native or modified sera obtained from transplant candidates with HLA class I sensitization were evaluated applying SAFB-based IgG, IgM, C1q, C1r, C1s, or C4 and C3 split product detection, respectively., Results: Evaluating a total of 1,164 single-antigen reactions, serum dilution (1:10) revealed an 11% incidence of the prozone effect as defined by a greater than 100% increase in IgG mean fluorescence intensity. Prozoning was found to be related to the amount of antibody-triggered C1q, C4 or C3 split product deposition, and was eliminated by serum modifications affecting the integrity of the C1 complex (dithiotreitol, ethylenediaminetetraacetic acid, heat inactivation). Remarkably, the same effect was achieved without C1 disintegration, either by serum treatment with methylamine to block C4 and C3 split product binding or by cobra venom factor to trigger C3 consumption., Conclusions: Our results reinforce a central role of C1 as a trigger of prozoning. However, we provide evidence that C1 may exert its effects only indirectly, namely via inducing C3 fragment deposition, which by coating of the bead surface may block the binding of IgG detection reagents.

Background: Human leukocyte antigen (HLA) mismatches are known to influence graft survival in deceased-donor kidney transplantation. We studied the effect of HLA mismatches in a population of recipients of deceased-donor or living-donor kidney transplantations., Methods: All 1998 transplantations performed in our center between 1990 and 2011 were included in this retrospective cohort study. Four different multivariable Cox proportional hazard analyses were performed with HLA mismatches as continuous variable, as categorical variable (total number of HLA mismatches), as binary variable (zero vs. nonzero HLA mismatches), and HLA-A, -B, and -DR mismatches included separately., Results: Nine hundred ninety-one patients received a deceased-donor kidney and 1007 received a living-donor kidney. In multivariable Cox analysis, HLA mismatches, recipient age, current panel-reactive antibodies, transplant year, donor age, calcineurin inhibitor treatment, and donor type were found to have a significant and independent influence on the risk of graft failure, censored for death. Variables representing the total number of HLA-A, -B, and -DR mismatches had a significant and comparable influence in all analyses., Conclusions: The influence of HLA mismatches on death-censored graft survival holds true for both deceased- and living-donor kidney transplantation. However, the relative risk of death-censored graft failure of a 2-2-2 mismatched living-donor kidney is comparable with that of a 0-0-0 mismatched deceased-donor kidney.

Background: Panel-reactive antibody (PRA) testing provides assessment of the breadth of sensitization a patient might have against human leukocyte antigen (HLA) antigens. The evolution of calculated PRA (cPRA) reflects the commitment of the transplant community to increase accessibility and promote equity to all patients awaiting kidney transplantation. Recent data from our center and others, however, suggested that a significant diversity of HLA-DQ antigens is not captured, which may lead to inequity in allocating cPRA points., Methods: HLA-DRB1-DQA1-DQB1 typing of 2182 individuals was evaluated for this study using Luminex-based sequence-specific oligonucleotide typing. A total of 3182 haplotypes were confirmed to have the level of resolution required for this study., Results: The diversity of HLA-DQαβ alleles is greater than what is apparent using the serologic equivalents. The distribution of these alleles within a serologic group varies, with some alleles being more frequent than others; therefore, their representation within the current cPRA system is inaccurate. Three informative examples are given. Haplotypes of DR antigens with DQαβ alleles did not always follow the common published linkage disequilibrium, especially in populations where there is greater genetic diversity., Conclusions: The current cPRA system does not take into account the distribution of molecular equivalents within DQ serologic specificities. This can result is inequitable allocation of sensitization points and disadvantaging the more sensitized patients. To ameliorate this situation, the United Network for Organ Sharing system should allow inputting HLA-DQαβ alleles both for donor typing and as antibody specificities, which will lead to better representation of unacceptable DQ alleles and improve organ allocation equity.

Background: Prognosis of renal transplants with positive flow cytometric crossmatch (FCXM) remains controversial., Methods: We analyzed the outcome of these kidney transplant recipients by human leukocyte antigen (HLA) donor-specific antibodies (HLA-DSA) using single-antigen bead (SAB) assays in major histocompatibility complex classes I and II. We compared them with controls with a negative FCXM., Results: Forty-five patients consecutively transplanted with a positive FCXM had significantly more acute rejection episodes than the control patients (33.3% vs. 8.9%, P=0.002). Risk of acute rejection was increased with day 0 (D0) positive T-cell FCXM (odds ratio [OR]=9.04, P=0.002), D0 positive B-cell FCXM (OR=7.43, P=0.02), and D0 HLA-DSA identified by SAB assay (OR=6.5, P=0.03). The 21 patients with D0 positive FCXM and D0 HLA-DSA had more acute rejection (62%, P=0.0001) and a lower estimated glomerular filtration rate 1-year posttransplantation (P=0.0001), when compared with controls. Mainly anti-Cw and anti-DP HLA-DSA were found in patients displaying acute rejection. The remaining FCXM-positive patients displayed short-term outcomes similar to controls. The presence of HLA-DSA detected only by the SAB assay in the context of a negative FCXM crossmatch was not associated with increased risk of acute rejection., Conclusion: Identification of HLA-DSA in D0 sera by the two sensitive techniques FCXM and SAB assay indicates which patients are at highest risk of subsequent acute allograft rejection and chronic allograft dysfunction.

Aim: Humoral sensitization affects transplant outcome, and it is now apparent that human leukocyte antigen (HLA) antibodies are specific for epitopes rather than antigens. Such epitopes can be structurally defined by HLAMatchmaker, an algorithm that considers eplets as critical elements of epitopes recognized by alloantibodies. This study addressed the question how mismatched HLA antigens induce specific antibodies in context with eplet differences with the antibody producer., Methods: HLA class I-specific human monoclonal antibodies derived from women sensitized during pregnancy were tested in Luminex assays with single allele panels. Their epitope specificity was determined from reactivity patterns and eplet differences between immunizing antigen and the antibody producer., Results: This study focuses on the reactivity patterns of 10 monoclonal antibodies specific for epitopes defined by a mismatched eplet paired with a self-eplet shared between immunizing HLA antigens and HLA antigens of the antibody producer. The eplets in these pairs are between 7 and 16 Å apart, a sufficient distance for contact by two separate complementarity-determining regions of antibody., Conclusions: These findings demonstrate that immunizing antigens have mismatched eplets that can form antibody-reactive epitopes with self-configurations on the molecular surface. They seem to suggest that HLA antibodies can be produced by autoreactive B cells that have undergone receptor editing to accommodate the recognition of nonself-eplets, the driving force of the humoral alloresponse. This concept enhances our understanding of structural epitope immunogenicity and the interpretation of antibody reactivity patterns with HLA panels.

Background: Data concerning the impact of human leukocyte antigen (HLA) compatibility on lung transplant survival rates are limited., Methods: Using the Collaborative Transplant Study database, 5-year graft outcome according to HLA mismatch was examined in 8020 deceased donor lung transplants performed during 1989 to 2009., Results: Graft survival rates showed a stepwise decrease as the combined number of HLA-A+B+DR mismatches increased from one to six (P<0.001). Surprisingly, the 28 grafts with 0 mismatches at all 3 loci had a 1-year survival rate of only 49.7%, significantly lower than for 1, 2, 3, 4, 5, or 6 mismatches (P=0.002, <0.001, <0.001, <0.001, 0.002, and 0.003, respectively). Multivariate regression analysis confirmed that, paradoxically, transplantation of grafts with zero HLA-A+B+DR mismatches was associated with a 19% increase in relative risk of failure. Donor lung preservation for up to 12 hr was not associated with inferior graft survival versus shorter preservation times (P=0.60)., Conclusions: Our data show that a high number of HLA mismatches or zero mismatches impacts unfavorably on lung transplant survival.

Background: Sensitized patients have a lower chance of receiving a crossmatch-negative kidney and, if transplanted, are at risk of antibody-mediated allograft rejection., Methods: For safe and timely transplantation of sensitized patients at our center, we developed an integrative algorithm that includes identification of high-risk patients, good human leukocyte antigen match, inclusion in the Eurotransplant Acceptable Mismatch Program when applicable, apheresis, anti-CD20 therapy, posttransplant antibody monitoring, and protocol biopsies. Thirty-four high-risk recipients of a deceased donor kidney (DDK: n=28) or living donor kidney (LDK: n=6) were transplanted using this algorithm., Results: One-year graft survival, death-censored graft survival, and patient survival rates in DDK recipients were 92.4%, 96.4%, and 95.8%, respectively. No graft loss or patient death was observed in the six LDK patients. Median serum creatinine at 1 year in DDK and LDK recipients was 1.2 and 1.4 mg/dL, respectively. Eleven DDK and three LDK patients experienced at least one biopsy-proven acute rejection episode, mostly showing borderline changes. Antibody-mediated rejection without graft loss was diagnosed in two DDK and one LDK patients. Delayed graft function was observed in 13 DDK and 1 LDK patients. Infectious complications were infrequent., Conclusions: We describe an algorithm for the categorization and treatment of presensitized high-risk patients. This protocol provides effective prevention of antibody-mediated rejection and is associated with a low rate of side effects and good graft outcome.

Background: This study evaluated the prognostic impact of pretransplant donor-specific anti-human leukocyte antigen antibodies (DSA) detected by single-antigen beads and compared the three generations of crossmatch (XM) tests in kidney transplantation., Methods: Thirty-seven T-cell complement-dependent cytotoxicity crossmatch (CXM) negative living donor kidney recipients with a retrospectively positive antihuman leukocyte antigen antibody screening assay were included. A single-antigen bead test, a flow cytometry XM, and a Luminex XM (LXM) were retrospectively performed, and the results were correlated with the occurrence of antibody-mediated rejections (AMRs) and graft function., Results: We found that (1) pretransplant DSA against class I (DSA-I), but not against class II, are predictive for AMR, resulting in a sensitivity of 75% and a specificity of 90% at a level of 900 mean fluorescence intensity (MFI); (2) with increasing strength of DSA-I, the sensitivity for AMR is decreasing to 50% and the specificity is increasing to 100% at 5200 MFI; (3) the LXM for class I, but not for class II, provides a higher accuracy than the flow cytometry XM and the B-cell CXM. The specificity of all XMs is increased greatly in combination with DSA-I values more than or equal to 900 MFI., Conclusions: In sensitized recipients, the best prediction of AMR and consecutively reduced graft function is delivered by DSA-I alone at high strength or by DSA-I at low strength in combination with the LXM or CXM.

Background: Posttransplant non-Hodgkin lymphoma is a rare complication but associated with high mortality. The extent to which human leukocyte antigen (HLA) mismatching influences the rate of posttransplant lymphoma has not been clarified., Methods: Data on lymphomas occurring in the first 3 years posttransplant were analyzed among first kidney transplants from deceased donors performed between 1985 and 2007 and reported to the Collaborative Transplant Study., Results: Of 152,728 patients included, 593 non-Hodgkin lymphomas were diagnosed. Cox multivariate regression analysis showed that HLA-A mismatches had no influence on the rate of lymphoma. One and two HLA-DR mismatches were associated with a hazard ratio (HR) of 1.21 (95% confidence interval 1.00-1.45, P=0.047) and 1.56 (95% confidence interval 1.21-1.99, P<0.001), respectively. For lymphoma of the kidney and central nervous system, HRs for two HLA-DR mismatches were 2.29 (P=0.007) and 2.17 (P=0.029), respectively. Two HLA-B mismatches were also significantly associated with lymphoma in the kidney (HR 2.82, P=0.009)., Conclusion: Mismatches at the HLA-DR locus are a significant risk factor for posttransplant non-Hodgkin lymphoma, particularly in the kidney and central nervous system, whereas two HLA-B mismatches increase the risk for the development of lymphoma of the kidney.

Introduction: National and regional strategies for allocating deceased heartbeating (DHB) donor kidneys to patients awaiting transplant are of great importance and have major implications for patients and healthcare systems. We describe the rationale for the 1998 National Kidney Allocation Scheme (1998 NKAS) and its impact on renal transplantation in the United Kingdom over 5 years., Methods: The 1998 NKAS was based on three tiers of patients defined by human leukocyte antigen (HLA) mismatch. This involved national allocation of well-matched kidneys in tiers 1 and 2, with regional allocation for less well-matched patients in tier 3. Pediatric patients (younger than 18 years) and regional patients were prioritized in tiers 1 and 2, with a points score based on six factors determining the specific priority order for allocation., Results: The 1998 NKAS allocated approximately half the kidneys from DHB donors to the national transplant list and resulted in significantly improved HLA matching, more than doubling the proportion of transplants that were 000 HLA-A, -B, and -DR mismatched from 7% to 16% for adults. Pediatric patients achieved comparable levels of HLA matching to adult patients for the first time in the United Kingdom through improved access to adult donor organs. The scheme also benefited highly sensitized patients and improved equity with regard to patient blood group, rareness of HLA type, and HLA homozygosity., Conclusion: The 1998 NKAS represented a significant advance for the allocation of DHB donor kidneys in the United Kingdom and, while not addressing inequities in access to transplant, it did largely achieve the principal goal of improving HLA matching.

Introduction: In 2004, it was agreed that a new allocation scheme for kidneys from deceased heart-beating donors was required in the United Kingdom to address observed inequities in access to transplant. The 2006 National Kidney Allocation Scheme (2006 NKAS) was developed to meet agreed objectives and preparatory work included a review of the criteria for human leukocyte antigen (HLA) matching and simulation evidence about the effectiveness of alternative schemes. ALGORITHM FOR 2006 NKAS: The 2006 NKAS gives absolute priority to all 000 HLA-A, -B, -DR-mismatched patients and well-matched pediatric patients (<18 years), and then a points score defines priorities for allocation with waiting time being most influential. Points for age and HLA mismatch are linked in a novel approach to ensure well-matched transplants for younger patients while recognizing that HLA matching is less important for older patients as retransplantation is less likely to be required. To improve equity for difficult to match patients, rare HLA specificities were defaulted to more common, related specificities. IMPACT OF 2006 NKAS: After 3 years, the scheme is already making good progress in achieving its objectives, with overall results similar to those observed in the simulations. There has been a significant benefit for patients waiting more than 5 years for transplant. A number of other advantages of the scheme are also apparent with equity of access improving in many respects, including the achievement of equity of access to transplant for HLA-DR homozygous patients, but geographical inequity of access will take a number of years to address fully.

Background and Objective: Clinical intestinal transplantation (Int-Tx) is limited by high rates of rejection, infection, and graft versus host disease. To improve clinical outcomes and eliminate the comorbidities associated with chronic immunosuppression, the induction of donor-specific tolerance to intestinal grafts is desirable, especially in the pediatric population. This study determined the ability of intestinal grafts to facilitate tolerance induction in major histocompatibility complex (MHC)-inbred miniature swine., Methods: Seven MGH-miniature swine received heterotopic intestinal grafts, two across MHC-matched, minor-antigen disparities, three across a class I MHC disparity with 12 days of cyclosporine A, and two across a class I MHC disparity without an immunosuppressant. Chimerism was assessed by FACS analysis and immunohistochemistry. Cell-mediated lympholysis assays were used to assess antidonor responses., Results: Two animals receiving intestinal grafts without an immunosuppressant developed antidonor IgG in 14 days and rejected these completely. All other grafts were accepted with 12 days of cyclosporine A across both MHC-matched and MHC class I barriers. Cell-mediated lympholysis assays showed donor-specific unresponsiveness by day 30 across MHC class I barriers. Greater than 15% peripheral donor cell chimerism persisted for more than 60 days after MHC-matched Int-Tx. Although less than 1.5% peripheral donor cell chimerism was seen during the maintenance period after class I-mismatched Int-Tx, 5% to 10% myeloid chimerism was found in the peripheral blood 14 to 90 days after Int-Tx. FACS analysis demonstrated that 1% to 2% of lymphocytes in the graft mesenteric lymph nodes were CD4/CD25(HIGH+)/Foxp3(+) cells., Conclusion: To our knowledge, this is the first demonstration of tolerance induction and persistence of chimerism in a large animal intestinal transplant model.

Background: Outcomes after deceased heart beating donor kidney transplantation are good, but survival rates vary according to a number of donor-, recipient-, and transplant-related factors. This comprehensive analysis of transplant outcomes was undertaken to inform development of a new Kidney Allocation Scheme., Methods: A complete case analysis of the outcome of kidney-only transplants in the United Kingdom, 1995 to 2001, was undertaken using Cox regression modeling. Seven thousand three hundred eighty-five (77%) of the 9585 transplants reported to the UK Transplant Registry were primary transplants in adults. Regrafts and pediatric patients (age <18 years) were analyzed separately. Transplant and patient survival over 5 years were investigated in addition to causes of prolonged cold ischemia time (CIT)., Results: A variety of factors significantly adversely influenced kidney transplant and patient outcome, including older donor age, older recipient age, waiting time to transplant over 2 years, diabetes, and earlier year of transplant. Human leukocyte antigen mismatch and CIT were significant in analyses of transplant but not in patient outcome, and an increased graft failure rate was also identified in adolescent patients. CIT was prolonged by long-distance kidney exchanges between centers (2 hr) and reallocation of kidneys for alternative patients (7 hr)., Conclusion: This study identified a number of factors that influence transplant outcome after deceased heart beating donor kidney transplant in the United Kingdom. The findings suggest that the influences of human leukocyte antigen mismatch and CIT are most relevant in considering a revised kidney allocation scheme.

Background: A pretransplant lymphocyte crossmatch (XM) test is usually considered mandatory but may delay deceased donor renal transplantation. We report on the safety and clinical efficacy of omitting the XM when it is predicted to be negative based on sensitization history and human leukocyte antigen-specific antibody screening., Methods: From 1998 to 2008, 606 deceased donor kidney transplants were performed at our center and the prospective donor-recipient XM omitted in 257 (42%). In all cases, a negative XM was confirmed retrospectively. Four hundred fourteen (68%) kidneys were donated after brain death (DBD) and 192 (32%) after cardiac death (DCD). The effect of this policy on cold ischemia time (CIT), delayed graft function (DGF), and transplant survival was assessed., Results: Mean CIT was 16.7 hr with a prospective XM and 14.3 hr when it was omitted (P<0.001). The beneficial effect of omitting the XM on DGF was only apparent in recipients of DBD kidneys, where the DGF rate was 28% with a prospective XM and 18% without a prospective XM (P=0.03). The corresponding DGF rate in recipients of DCD kidneys was 52% with a prospective XM and 54% without a prospective XM. Logistic regression analysis, after adjustment for variables that influenced DGF, showed that the odds on suffering DGF were lower when the pretransplant XM test was omitted (P=0.04). Neither acute rejection rate nor long-term graft survival was influenced by omission of the XM., Conclusion: Rigorous recording of potential allosensitizing events and comprehensive antibody screening allows the XM to be safely omitted in selected patients and this helps limit CIT and may reduce DGF.

Background: Fully human leukocyte antigens (HLA)-mismatched liver grafts are well accepted, but the HLA influence on acceptance or rejection is unclear and much less so the impact of HLA-C, which may be conditioned by the fact that HLA-C-encode molecules are the major ligands for killer cell immunoglobulin-like receptors (KIR)., Methods: The HLA-C allele compatibility and the effect of donor and recipient HLA-C genotype on early liver graft acceptance and on CD8KIR T-cells recuperation were analyzed in a series of 431 primary liver transplants. Standard polymerase chain reaction PCR-SSO was used for HLA-C typing and flow cytometry to identify T cells KIR positives. Transplants were classified into two groups: acute rejection and nonacute rejection, and individual HLA-C genotypes as C1/C1, C2/C2, and C1/C2., Results: A favorable effect of HLA-C allelic compatibility on early liver graft acceptance was found because acute rejection significantly increased in transplants performed with 2 HLA-C allele mismatches (P=0.02). Considering the HLA-C groups, it was observed that C1/C2 heterozygous donors were best accepted in C1/C1 patients than in C2/C2 recipients, who experienced a high rate of acute rejection (P<0.004 and P<0.005, respectively). In addition, after transplantation CD3CD8KIR2D T-cells repertoires significantly increased in C1/C1 and C1/C2, but not in C2/C2 patients., Conclusions: This study confirms the benefit of HLA-C allele matching on early liver transplant outcome and shows that donor HLA-C heterozygosis influences the alloresponse of C1 and C2 homozygous patients and the recuperation of CD3CD8KIR2D T cells, suggesting an involvement in liver graft tolerance.

Background: Several reports showed a contribution of anti-MICA (major histocompatibility complex class I chain-related molecule A) antibodies (Abs) to the development of acute and chronic rejection. Identification of the epitopes to which the Abs bind may help to determine immunoreactive regions essential for the major histocompatibility complex compatibility between donor and recipients, leading to the best outcome of the transplant., Methods: Sera from 284 kidney transplant patients were screened for anti-MICA Abs by Luminex assay. MICA allele typing of the recipients was determined. The epitopes of MICA were mapped by screening a synthesized library of overlapping peptides from the extracellular domains of the protein against the sera from kidney transplant patients with anti-MICA Abs., Results: Antibodies against MICA were detected in 50 of 284 patients (17.6%) and correlated with the development of acute rejection. Nine antigenic regions were immunoreactive with anti-MICA Abs in the sera samples. Four of these continuous epitopes mapped to polymorphic amino acids (aa). Five antigenic regions were shared epitopes found in all the MICA alleles. The polymorphic residues, 173 (E/K), 175 (S/G), and 181 (R/T), had determined allele-specific epitopes (reactivity patterns 1 and 2). In contrast, the aa 208Y and 213T were implicated in the cross-reactivity among alleles., Conclusions: The presence of anti-MICA Abs could be an important marker for diagnosis because of their contribution to the outcome of the graft, regardless of presence of anti-HLA Abs. Additionally, the identification of epitopes revealed the in vivo antigens of the transplant and is spurring the development of new matching strategies to reduce the incidence of acute and chronic rejection.

Background: Defining the clinical relevance of donor-specific HLA-antibodies detected by single-antigen flow-beads (SAFB) is important because these assays are increasingly used for pretransplant risk assessment and organ allocation. The aims of this study were to investigate to which extent HLA-DSA detected by SAFB represent a risk for antibody-mediated rejection (AMR) and diminished allograft survival, and to define HLA-DSA characteristics predictive for AMR., Methods: In this retrospective study of 334 patients with negative complement-dependent cytotoxicity crossmatches, day-of-transplant sera were analyzed by SAFB, HLA-DSA determined by virtual crossmatching, and the results correlated with the occurrence of AMR and allograft survival., Results: Sixty-seven of 334 patients (20%) had HLA-DSA. The incidence of clinical/subclinical AMR at day 200 posttransplant was significantly higher in patients with HLA-DSA than in patients without HLA-DSA (55% vs. 6%; P<0.0001). Notably, 30/67 patients with HLA-DSA (45%) did not experience clinical/subclinical AMR. Death-censored 5-year allograft survival was equal in patient without HLA-DSA and patients with HLA-DSA but no AMR (89% vs. 87%; P=0.95), whereas it was 20% lower in patients with HLA-DSA and AMR (68%; P=0.002). The number, class, and cumulative strength of HLA-DSA determined by SAFB, and prior sensitizing events were not predictive for the occurrence of AMR., Conclusions: These results support the utility of SAFB for pretransplant risk assessment and organ allocation, and suggest that improvement of the positive predictive value of HLA-DSA defined by SAFB will require an enhanced definition of pathogenic factors of HLA-DSA.

Background: Although the incidence of early acute rejection could have been diminished in the past, the long-term renal allograft survival could not benefit from the introduction of more effective immunosuppressive regimens mainly aiming at cellular rejection mechanisms. The cause of chronic rejection is still discussed controversially. Here, we demonstrate to what extent human leukocyte antigen (HLA) antibodies (HLAab) posttransplant contribute to late graft outcome., Methods: A total of 1014 deceased kidney transplant recipients transplanted at the Charité hospital were monitored in a cross-sectional manner for the development of HLAab using Luminex Single Antigen beads. Patients with stable kidney function at a median of 5-years posttransplant were tested once for HLAab and monitored for 5.5 years after testing., Results: Thirty percent of recipients showed HLAab. Donor-specific antibodies (DSA) were found in 31% of antibody positive patients. The presence of DSA was associated with a significantly lower graft survival of 49% vs. 83% in the HLAab negative group (P< or =0.0001). Non-DSAs also had an adverse effect on graft survival (70% vs. 83%; P=0.0001). In a prospective analysis of 195 patients with repeatedly no detectable HLAab, the survival probability was 94% as opposed to 79% survival among patients who developed HLAab de novo after the first testing (P=0.05)., Conclusions: We confirmed that HLAab produced even late after transplantation are detrimental to graft outcome. DSA were proven to have a strong adverse impact on graft survival. The results indicate that a posttransplant HLAab monitoring routine could be appropriate to improve long-term results.

Background: After human leukocyte antigen (HLA) antibody-incompatible transplantation, donor specific and third party HLA antibodies may be found, and their levels fall in a donor-specific manner during the first month. However, these changes have not been previously described in detail., Methods: Donor-specific HLA antibody (DSA) and third-party HLA antibody (TPA) levels were measured using the microbead method in 44 presensitized patients who had renal transplantation., Results: DSA+TPA fell in the first 4 days after transplantation, and greater falls in DSA indicated absorption by the graft. This occurred for class I (57.8% fall compared with 20.2% for TPA, P<0.0005), HLA DR (63.0% vs. 24.3%, P<0.0004), and for HLA DP/DQ/DRB3-4 (34% vs. 17.5%, P=0.014). Peak DSA levels occurred at a mean of 13 days posttransplant, and they were higher than pretreatment in 25 (57%) patients and lower in 19 (43%) patients (P=ns). The risk of rejection was associated with peak DSA levels; 15 of 25 (60%) patients with DSA at median fluorescence intensity (MFI) more than 7000U experienced rejection, compared with 4 of 7 (57%) patients with peak DSA MFI 2000 to 7000U, and 2 of 12 (17%) patients with peak DSA MFI less than 2000U (P<0.02). DSA levels subsequently fell in a donor specific manner compared to TPA., Conclusion: DSA levels may change markedly in the first month after antibody incompatible transplantation, and the risk of rejection was associated with higher pretreatment and peak levels.

Sensitized patients awaiting renal transplantation have a markedly reduced probability of receiving a crossmatch (XM)-negative renal allograft, and, even if transplanted with a negative complement-dependent cytotoxicity (CDC)-XM, they are at an increased risk of antibody-mediated humoral rejection with early graft loss. We report here for the first time on the effectiveness of a single pretransplant plasma exchange session in rendering a positive complement-dependent cytotoxicity-XM negative and, in combination with anti-CD20 therapy, allowing successful renal transplantation in two sensitized deceased-donor kidney allograft recipients. In a third patient with high donor-specific reactivity, the therapy was unsuccessful. Plasma exchange treatments were continued during the posttransplant period until stable allograft function was achieved. Both patients showed good graft outcome at 27 and 21 months after transplantation with serum creatinine values of 1.60 and 1.25 mg/dL, respectively.

Background: Despite their clinical importance, clinical routine tests to detect anti-endothelial cell antibodies (AECA) in organ transplantation have not been readily available. This multicenter prospective kidney transplantation trial evaluates the efficacy of a novel endothelial cell crossmatch (ECXM) test to detect donor-reactive AECA associated with kidney allograft rejection., Methods: Pretransplant serum samples from 147 patients were tested for AECA by a novel flow cytometric crossmatch technique (XM-ONE) using peripheral blood endothelial progenitor cells as targets. Patient enrolment was based on acceptance for transplantation determined by donor lymphocyte crossmatch results., Results: Donor-reactive AECA were found in 35 of 147 (24%) patients. A significantly higher proportion of patients with a positive ECXM had rejections (16 of 35, 46%) during the follow-up of at least 3 months compared with those without AECA (13 of 112, 12%; P<0.00005). Both IgG and IgM AECAs were associated with graft rejections. Mean serum creatinine levels were significantly higher in patients with a positive ECXM test at 3 and 6 months posttransplant., Conclusions: XM-ONE is quick, easy to perform on whole blood samples and identifies patients at risk for rejection and reduced graft function not identified by conventional lymphocyte crossmatches.

Background: The requirement for a prospective crossmatch limits some organ allocation to local areas. The delay necessitated by the crossmatch restricts the distance across which offers can be made without unduly increasing the ischemia time. A collaborative study involving 14 transplant centers was undertaken by the Organ Procurement and Transplantation Network/United Network for Organ Sharing (OPTN/UNOS) Histocompatibility Committee to evaluate the accuracy with which the detection of unacceptable human leukocyte antigen (HLA) antigens by most advanced solid phase immunoassays can predict crossmatch results. In addition, using actual patients' unacceptable HLA antigens, the number of compatible donors that would have been available from the OPTN deceased kidney donors during 2002 to 2004 were investigated., Methods: Panel reactive antibodies were performed by conventional or solid phase assays, and crossmatches were performed by cytotoxicity or flow cytometry. Analyses were stratified for T and B cell and by method of identifying unacceptable HLA antigens and crossmatch techniques., Results: Combination of solid phase immunoassays and flow cytometry crossmatches resulted in a higher prediction rates of positive T cell (86.1%-93.5%) and B-cell crossmatches (91%-97.8%). Prediction of negative crossmatches based on different combination of panel reactive antibodies and crossmatch techniques varied from 14.3% to 57.1%. Furthermore, numerous potential compatible donors were identified for each patient, regardless of their ethnicity, in the OPTN database, when predicted incompatible ones were excluded., Conclusions: The above results showed that with the advent of solid phase immunoassays, HLA antibodies can now be accurately detected resulting in prediction of crossmatch outcome. This should facilitate organ allocation and prevents shipment of organs to distant incompatible recipients.