Influence of Test Technique on Sensitization Status of Patients on the Kidney Transplant Waiting List

The exquisitely sensitive single antigen bead (SAB) technique was shown to detect human leukocyte antigen (HLA) antibodies in sera of healthy male blood donors. Such false reactions can have an impact on critical decisions, especially with respect to the determination of unacceptable HLA‐antigen mismatches in patients awaiting a kidney transplant. We tested pretransplant sera of 534 patients on the kidney waiting list using complement‐dependent cytotoxicity (CDC), enzyme‐linked immunosorbent assay (ELISA) and SAB in parallel. Evidence of HLA antibodies was obtained in 5% of patients using CDC, 14% using ELISA, and 81% using SAB. Among patients without history of an immunizing event, 77% showed evidence of HLA antibodies in SAB. In contrast 98% of these patients were negative in ELISA and CDC. In patients without an immunizing event, SAB‐detected antibodies reacted not always weakly but with mean fluorescence intensity (MFI) values as high as 14 440. High‐MFI‐value antibodies were found in some of these patients with HLA specificities that are rather common in general population, consideration of which would lead to unjustified exclusion of potential kidney donors. False SAB reactions can be unveiled by testing with additional antibody assays. Denial of donor kidneys to recipients based on HLA‐antibody specificities detected exclusively in the SAB assay is not advisable.     

Clinical Significance of Pretransplant Donor‐Specific Antibodies in the Setting of Negative Cell‐Based Flow Cytometry Crossmatching in Kidney Transplant Recipients

Antibodies to donor‐specific HLA antigens (donor‐specific antibodies [DSA]) detected by single‐antigen bead (SAB) analysis prior to kidney transplant have been associated with inferior graft outcomes. However, studies of pretransplant DSA, specifically in the setting of a negative flow cytometry crossmatch (FCXM) without desensitization therapy, are limited. Six hundred and sixty kidney and kidney–pancreas recipients with a negative pretransplant FCXM from September 2007 to August 2012 without desensitization therapy were analyzed with a median follow‐up of 4.2 years. All patients underwent cell‐based FCXM and SAB analysis on current and historic sera prior to transplantation. One hundred and sixty‐two patients (24.5%) had DSA detected prior to transplant. One‐year acute rejection rates were similar in DSA‐positive versus DSA‐negative patients (15.4% vs. 11.4%, respectively; p = 0.18) and were higher in those with DSA mean fluorescence intensity (MFI) greater than or equal to 3000 in multivariable analysis (p = 0.046). The estimated glomerular filtration rate (eGFR) at 3 and 4 years was lower in the DSA(+) versus the DSA(?) group (p = 0.050 at 3 years) without an impact on 5‐year death‐censored graft survival (89.0% vs. 90.6%, respectively; p = 0.53). Timing (current or historic) of DSA detection did not alter these findings. In conclusion, pretransplant DSA in the setting of a negative FCXM confers minimal immunologic risk in the intermediate term, does not necessitate desensitization therapy and should not represent a barrier to renal transplant.     

Blood levels of donor-specific human leukocyte antigen antibodies after renal transplantation: resolution of rejection in the presence of circulating donor-specific antibody

BACKGROUND: Accommodation to antibody is an important mechanism in successful ABO-incompatible transplantation, but its importance in human leukocyte antigen (HLA) antibody-incompatible transplantation is less clear, as sensitive techniques facilitating daily measurement of donor-specific HLA antibodies (DSAs) have only recently been developed. METHODS: We report 24 patients who had HLA antibody-incompatible kidney transplantation (21 living donors, 3 deceased), 21 of whom had pretransplant plasmapheresis. Eight had positive complement-dependent cytotoxic (CDC) crossmatch (XM) pretransplant plasmapheresis, nine had positive flow cytometric (FC) XM, and seven had DSA detectable by microbead analysis only. After transplant, DSA levels were monitored closely with microbead assays. RESULTS: Rejection occurred in five of eight (62.5%) CDC-positive cases, in three of nine (33%) FC-positive cases, and in two of seven (29%) of microbead-only cases at a median of 6.5 days after transplantation. Resolution occurred at a median of 15 days after transplantation, in 8 of 10 cases when the microbead level of DSA had median fluorescence intensity (MFI) >2000 U, in 6 of 10 when the microbead MFI >4000 U. In 8 of 10 cases, the microbead MFI at the time of resolution was greater than at the onset. DSA did not always cause clinical rejection. In five cases with a posttransplant DSA peaking at MFI >2000 U on microbead assay, rejection did not occur. CONCLUSION: These data suggest that the dominant method of successful transplantation was function of the transplant in the presence of circulating DSA, and they also define the period during which this occurred.     

Determining donor‐specific antibody C1q‐binding ability improves the prediction of antibody‐mediated rejection in human leucocyte antigen‐incompatible kidney transplantation

Detrimental impact of preformed donor‐specific antibodies (DSAs) against human leucocyte antigens on outcomes after kidney transplantation are well documented, however, the value of their capacity to bind complement for predicting antibody‐mediated rejection (AMR) and graft survival still needs to be confirmed. We aimed to study DSA characteristics (strength and C1q binding) that might distinguish harmful DSA from clinically irrelevant ones. We retrospectively studied 60 kidney‐transplanted patients with preformed DSA detected by single antigen bead (SAB) assays (IgG and C1q kits), from a cohort of 517 kidney graft recipients (124 with detectable anti‐HLA antibodies). Patients were divided into DSA strength (MFI < vs. ≥ 15 000) and C1q‐binding ability. AMR frequency was high (30%) and it increased with DSA strength (P = 0.002) and C1q+ DSA (P < 0.001). The performance of DSA C1q‐binding ability as a predictor of AMR was better than DSA strength (diagnostic odds ratio 16.3 vs. 6.4, respectively). Furthermore, a multivariable logistic regression showed that C1q+ DSA was a risk factor for AMR (OR = 16.80, P = 0.001), while high MFI DSAs were not. Graft survival was lower in high MFI C1q+ DSA in comparison with patients with C1q? high or low MFI DSA (at 6 years, 38%, 83% and 80%, respectively; P = 0.001). Both DSA strength and C1q‐binding ability assessment seem valuable for improving pretransplant risk assessment. Since DSA C1q‐binding ability was a better predictor of AMR and correlated with graft survival, C1q‐SAB may be a particularly useful tool.     

Positive virtual crossmatch with negative flow crossmatch results in two cases

Pre-transplant (Tx) presence of HLA antibodies (HLA-Ab) especially donor specific antibodies (DSA) has been correlated with post-Tx rejection. While crossmatch (XM) is the specific method to identify DSA, logistical reasons prevent performing a prospective XM in all transplants. In such cases DSA as identified by solid-phase assay (SPA) are being used to perform a virtual crossmatch (VXM). We present two cases, a heart-lung transplant and a kidney transplant, for which testing detected a presumptive DSA with discordant results: a negative flow cytometric crossmatch (FXM) and a positive VXM using SPA. The subsequent investigation determined the antibody, in both cases, was presumably directed against an epitope of a HLA-B*44 antigen found on the single antigen beads (SAB) used in the SPA but not against the native form on the donor lymphocytes used in the FXM. Manufacturing of SAB beads results in denaturation of epitopes, majority of which are removed from the final product, but residual amount is present on the final product. Denaturation of majority of antigen epitopes on single antigen beads did not remove the activity of the recipient's antibodies but it did diminish the activity of positive control serum. This indicates denaturation of some of the HLA-B*44 antigen during manufacturing of the SAB may have lead to the reactivity. Antibody mediated rejection does not appear to be associated with the titer of this antibody to denatured antigen in the first case and so clinical relevance of such antibodies is unclear. Subsequently a second case of discordant FXM and VXM was identified in a potential kidney transplant patient who went on to an uneventful transplant. In this case, lymphocytes from the donor were positively shown to express HLA-B*44:02 using known anti- HLA-B*44:02 control serum. Platelets identified as HLA-B*44:02 could adsorb the anti-HLA-B*44:02 from the control serum activity but not from that of the recipient's anti- HLA-B 44 antibody adding evidence that this antibody should best be classified as a false positive finding. The presence of such an antibody if misidentified may result in unnecessary therapy being instituted or the inappropriate denial of an organ for transplantation.     

Shared Molecular Eplet Stimulates Acute Antibody-Mediated Rejection in a Kidney Transplant Recipient With Low-Level Donor-Specific Antibodies: A Case Report

HLA antibodies usually recognize epitopes rather than antigens. This case report reveals that acute antibody-mediated rejection (AMR) that occurred in a kidney transplant recipient with low-level donor-specific antibodies (DSAs) could be explained by shared epitope. A 39-year-old woman received a first kidney transplant from a deceased donor (HLA-DRB1*11:06, *12:02, DRB3*02:02, *03:01). She developed acute AMR confirmed by kidney biopsy on day 4 after transplantation. Antibody testing with pretransplant serum showed anti-DR11 DSA below cutoff level (mean fluorescence intensity [MFI], 702; cutoff >1,000). However, high-level DSAs were detected on day 5 after transplantation (anti-DR11 MFI, 8,531; anti-DR12 MFI, 3,146). We hypothesized that the sharp rise in DSA levels was a result of anamnestic response with donor-antigen sensitization that occurred during pregnancy. High-resolution HLA-DR typing of her husband showed HLA-DRB1*03:01, *15:02:01, DRB3*02:02, DRB5*01:02. No sharing between donor HLAs eliciting reactive antibodies and her husband's HLAs was detected. Nevertheless, we speculated that shared epitope, not antigen, was the cause of allosensitization. To identify the shared epitope recognized by patient's antibodies, we used HLAmatchmaker, a computer algorithm that considers small configurations of polymorphic residues referred to as eplets as essential components of HLA epitopes for analysis. The results showed that 149H, which was the eplet shared by HLA-DRB1*03:01 (from her husband) and DRB1*11:06, DRB1*12:02, DRB3*03:01 (from donor), was the most prevalent eplet on DRB1 reactive alleles in Luminex assay. In conclusion, pretransplant low-level DSAs can induce AMR early after transplantation as a result of shared epitopes with a previous immunizer.     

The correlation of results of panel reactive antibody,identification, and single antigen beads in detection of anti-HLA antibodies: Istanbul Faculty of Medicine,tissue typing laboratory experience

BackgroundWe have performed a retrospective analysis of anti-HLA class I MHC and class II MHC antibodies measured using a single antigen bead (SAB) assay and a panel reactive antibody (PRA) assay.Material and methodsA group of 256 patients with end-stage renal disease (ESRD) was tested for anti-HLA antibodies in the tissue typing laboratory between 2017 and 2020. In the cohort, the serum samples of patients waiting for transplantation were tested. Both the PRA and SAB tests of these patients were analyzed using the Luminex (Immucor) method. The threshold of positivity was accepted as median fluorescence intensities (MFI) ≥1000 for PRA screening and MFI ≥750 for SAB screening.ResultsOverall, antibodies to HLA antigens were detected in 202 (78.9%) out of 256 patients in the PRA study. Antibodies against both class I/II antigens were detected only in 15.6% of these patients, whereas antibodies against only against class I HLA in 31.3% and only against class II HLA in 32.0%. By comparison, the SAB study found that 66.8% of patients were positive for HLA antigens. Furthermore, donor-specific antibodies (DSA) were detected in 52.0% of PRA-positive patients and 52.6% of SAB-positive patients. It was shown that 168 patients (83.2%) out of 202 PRA-positive patients were found to be SAB-positive. In addition, 51 patients negative in the SAB assay (94.4%) were also negative in the PRA assay. Statistical analysis established a significant correlation between the PRA and SAB positivity (p > 0.001).It was also shown that MFI ≥3000 PRA positivity for class I HLA antigens (p = 0.049) and MFI ≥5000 PRA positivity for class II antigens (p < 0.001) correlated with the SAB positivity in patients.ConclusionOur results showed the importance of both PRA and SAB assays to define the status of sensitization in patients.     

High Risk of Sensitization After Failed Islet Transplantation

Human Leukocyte Antigen (HLA) antibodies posttransplant have been associated with an increased risk of early graft failure in kidney transplants. Whether this also applies to islet transplantation is not clear. To achieve insulin independence after islet transplants multiple donor infusions may be required. Hence, islet transplant recipients are at risk of sensitization after transplantation. Islet transplant recipients were screened for HLA antibodies posttransplant by flow-based methods. A total of 98 patients were studied. Twenty-nine patients (31%) developed de novo donor specific antibodies (DSA) posttransplant. Twenty-three patients developed DSA while on immunosuppression (IS). Among recipients who have discontinued IS, 10/14 (71%) are broadly sensitized with panel reactive antibody (PRA) >or=50%. The risk of becoming broadly sensitized after transplant was 11/69 (16%) if the recipient was unsensitized prior to transplant. The majority of these antibodies have persisted over time. Appearance of HLA antibodies posttransplant is concerning, and the incidence rises abruptly in subjects weaned completely from IS. This may negatively impact the ability of these individuals to undergo further islet, pancreas or kidney transplantation and should be discussed upfront during evaluation of candidates for islet transplantation.     

Interpretation of HLA single antigen bead assays

The introduction of single antigen bead (SAB) assays for detection and quantitation of HLA antibodies has improved our ability to identify and manage allosensitized transplant candidates and recipients and to improve organ allocation, and was critical to the creation of national paired kidney exchanges. The principal limitations of the technology have been detailed in the literature and include artifacts resulting in non-specific background, variability, lack of standardization, and interpretive challenges. Accurate interpretation of SAB assays requires consideration of a number of factors, including identification of epitope reactivity patterns, mean fluorescence intensity (MFI) values, patient history, and appreciation of individual bead and assay nuances. The MFI value provides an estimate of relative HLA antibody levels although limited by saturation and epitope distribution effects. A better understanding of SAB assays and MFI values will be necessary to ensure appropriate application of these assays clinically and a higher quality of antibody data used in support of published clinical studies.     

Clinical significance of low pre-transplant donor specific antibodies (DSA) in living donor kidney recipients with negative complement-dependent cytotoxicity crossmatches (CDCXM), and negative flow cytometry crossmatches (FLXM) – A single-center experience

BackgroundIt is controversial whether all donor-specific antibodies (DSA) detected by the solid-phase single antigen bead (SAB) assay negatively affect kidney transplantation outcomes. The study aimed to evaluate the possible clinical significance of low pre-transplant DSA in living donor kidney recipients. We analyzed a group of patients with HLA-A, B, and -DR DSA reactivities below a virtual crossmatch (VXM) value of 5000 MFI but with all VXM DSA reactivities at HLA-DQ, -DP, and -Cw, which were not typed routinely for donors prior to transplantation. We also investigated the incidence of persistent and de novo DSAs in available posttransplant SAB assays.MethodsFrom the historical cohort of living donor recipients transplanted between 2014 and 2018 at our center (n = 82), 55 patients met the inclusion criteria, namely: these patients were > 18 years old with non-HLA identical sibling donors, who were not desensitized, who had available pre-transplant SAB results, and who had negative both complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FLXM) results. An additional donor HLA typing, performed for all 55 recipients, identified donor additional HLA-DQ, -DP, and -Cw DSA reactivities. These patients were then divided by SAB reactivity into three groups: 1) those with DSA-positive reactivities; 2) those with non-donor-specific anti-HLA reactivities (NDSA); and, 3) those who were anti-HLA-negative. All these recipients were followed for three years and checked for their de novo or persistent DSA.ResultsIn the studied cohort, DSA-positive, NDSA reactive, and anti-HLA negative recipients constituted 33%, 36%, and 31% of 55 patients, respectively. Non-routinely considered pre-transplant HLA-DQ, -DP, and -Cw DSA-positive reactivities were shown in as many as 78% of DSA-positive cases (group 1) with the lowest MFI value of 319 to DP4 and the highest MFI of 5767 to DQ2. Of the pre-transplant HLA-A, B, and -DR DSA reactivities, only -DR52 DSA reactivity reached the highest MFI value of 2191. These detected DSAs did not reduce the mean estimated glomerular filtration rate (eGFR) values and did not increase the incidence of proteinuria in recipients. While the 3-year graft survival was lower in the DSA-positive group (94.4%) with one recipient who lost kidney transplant, the difference was not significantly different (p = 0.7) from the NDSA (100%) and negative (100%) groups. In terms of the incidence of de novo acute antibody-mediated rejection (AMR) at three years after transplantation, no case has been reported in the cohort. This may suggest that low DSA-positive recipients do not experience higher rejection rate. However, DSA-positive recipients had a tendency for a higher frequency of C4d deposits in peritubular capillaries (PTC) and de novo DSA.ConclusionOur 3-year follow-up of patients with low pre-transplant DSA found no association with a deterioration in graft function and worse graft survival. Furthermore, we did not observe an increase in AMR in our patients with low DSA. A larger cohort and a longer follow-up period may be needed to evaluate the tendency of low DSA-positive recipients towards the higher incidence of C4d deposits in PTC and/or de novo DSA.     

Antibody-mediated rejection owing to donor-specific HLA-DQA1 antibodies after renal transplantation: A case report

BackgroundDonor-specific HLA antibodies are important risk factors in antibody-mediated rejection and graft loss after renal transplantation and are associated with higher rejection rates and lower graft survival. Most de novo donor specific antibodies (dnDSA) after renal transplantation are directed toward donor HLA-DQ antigens. An HLA-DQ antigen is a heterodimer consisting of an alpha and beta chain. Traditionally, HLA-DQA1 typing has not been part of pretransplant evaluation. Therefore, DQ alpha proteins are not usually considered in the interpretation of HLA-DQ antibody reactions.MethodsThe renal transplant recipient had a 0% panel reactive antibody pretransplant. Two years after transplantation, he developed symptoms of abdominal distension and bilateral lower extremity edema. Histopathological findings on renal puncture biopsy showed a combination of T-cell-mediated acute rejection type IIA and antibody-mediated rejection with a trend toward chronicity in the transplanted kidney. DSAs were investigated by HLA-I (HLA-A/B) and HLA-II (HLA-DRB1/DQA1/DQB1) single antigen bead (SAB) assay. HLA typing was performed to explain the antibody reactivity patterns by PCR-SSO and Sequencing-based typing (SBT). HLAMatchmaker analysis was performed to identify eplets that explain antibody reactivity patterns.ResultsHLA-II SAB analysis of the patient's serum at the time of rejection showed positive reactions with all DQB1*03:03-carrying beads with high mean fluorescence intensity (MFI). However, DQB1*03:03 was not a dnDSA antigen. High-resolution HLA typing revealed that HLA-DQA1*05:01 and DQA1*03:02 were mismatched donor antigens. HLA Matchmaker analysis demonstrated reactivity toward 130R and 116 V eplet on DQA1 and DQB1.ConclusionsAntibodies specific to DQα chains after renal transplantation were highlighted.     

Bortezomib as the Sole Post‐Renal Transplantation Desensitization Agent Does Not Decrease Donor‐Specific Anti‐HLA Antibodies

Persistence of donor‐specific anti‐HLA antibodies (DSA) associated with antibody‐mediated graft injuries following kidney transplantation predicts evolution toward chronic humoral rejection and reduced graft survival. Targeting plasma cells, the main antibody‐producing cells, with the proteasome inhibitor bortezomib may be a promising desensitization strategy. We evaluated the in vivo efficacy of one cycle of bortezomib (1.3 mg/m²× 4 doses), used as the sole desensitization therapy, in four renal transplant recipients experiencing subacute antibody‐mediated rejection with persisting DSA (>2000 [Mean Fluorescence Intensity] MFI). Bortezomib treatment did not significantly decrease DSA MFI within the 150‐day posttreatment period in any patient. In addition, antivirus (HBV, VZV and HSV) antibody levels remained stable following treatment suggesting a lack of efficacy on long‐lived plasma cells. In conclusion, one cycle of bortezomib alone does not decrease DSA levels in sensitized kidney transplant recipients in the time period studied. These results underscore the need to evaluate this new desensitization agent properly in prospective, randomized and well‐controlled studies.     

Early findings of prospective anti‐HLA donor specific antibodies monitoring study in pancreas transplantation: Indiana University Health Experience

The significance of donor‐specific antibodies (DSA) is not well known in the setting of pancreas transplantation. Since December 2009, we prospectively followed pancreas transplant patients with single‐antigen‐luminex‐bead testing at one, two, three, six, and then every six months for the first two yr. Thirty‐five of the 92 patients that underwent pancreas transplantation (13 pancreas‐alone [PTA], 20 with a kidney [SPK], and two after a kidney [PAK]) agreed to participate in study. Median age at transplant was 45 yr and follow‐up was 23 months. Majority were Caucasian (n = 33) and male (n = 18). Rabbit anti‐thymocyte globulin induction was used. Median HLA‐mismatch was 4.2 ± 1.1. Eight patients (7SPK, 1PAK) developed post‐transplant DSA at median follow‐up of 76 d (26–119), 1 SPK had pre‐formed DSA. Seven patients had both class I and class II DSA, one with class I and one with class II only. Mean peak class I DSA‐MFI was 3529 (±1456); class II DSA‐MFI was 5734 (±3204) whereas cumulative DSA MFI (CI + CII) was 9264 (±4233). No difference was observed in the patient and donor demographics among patients with and without DSA. One patient in non‐DSA group developed acute cellular rejection of pancreas. From our data it appears that post‐transplant DSA in pancreas allograft recipients may not impact the early‐pancreatic allograft outcomes. The utility of prospective DSA monitoring in pancreatic transplant patients needs further evaluation and long‐term follow‐up.     

供者特异性抗体监测在肾移植中的应用

目的 研究肾移植术后受者血清中供者特异性抗体（DSA）与发生急性排斥反应的关系,为临床早期诊断、合理制定个体化治疗方案、评估疗效提供客观的参考依据.方法 选取2012年1月至2013年8月西安交通大学医学院第一附属医院肾病医院肾移植科285例首次肾移植受者,术后动态监测DSA水平,检测时间点为术后3,5,7,14,21,30,60,90 d.观察受者肾功能和急性排斥反应发生情况.使用卡方检验或Fisher精确概率法比较不同HLA抗体类型的受者急性排斥反应发生率.结果 285例肾移植受者术后初筛人类白细胞抗原（HLA）抗体阳性率为22.11％ （63/285）,其中DSA阳性4例.急性排斥反应发生率6.67％ （19/285）.HLA抗体阴性受者和HLA抗体阳性且DSA阴性受者急性排斥反应发生率分别为3.15％ （7/222）和16.95％ （10/59）,二者相比差异有统计学意义（x2=12.891,P＜0.05）;4例DSA阳性受者有3例发生急性排斥反应,与HLA抗体阴性、HLA抗体阳性且DSA阴性受者急性排斥反应发生率相比,差异均有统计学意义（P=0.000和P=0.016）.19例发生急性排斥反应受者经甲泼尼龙、兔抗人胸腺细胞免疫球蛋白冲击治疗或血浆置换等治疗后,15例受者成功逆转,1例死于并发症.结论 动态监测肾移植术后受者DSA水平,可预测移植肾功能状态,对急性排斥反应的发生有重要预警作用,有利于及时清除或降低DSA水平,对有效预防和及时诊治排斥反应具有重要作用。     

Pretransplant human leukocyte antigen antibodies detected by single‐antigen bead assay are a risk factor for long‐term kidney graft loss even in the absence of donor‐specific antibodies

Clinical relevance of ELISA‐ and single‐antigen bead assay (SAB)‐detected pretransplant HLA antibodies (SAB‐HLA‐Ab) for kidney graft survival was evaluated retrospectively in 197 patients transplanted between 2002 and 2009 at the University Clinic Frankfurt. Having adjusted for retransplantation and delayed graft function, a significantly increased risk for death‐censored graft loss was found in patients with pretransplant SAB‐HLA‐Ab [HR: 4.46; 95% confidence interval (CI): 1.47–13.48; P = 0.008]. The risk for increased graft loss was also significant in patients with pretransplant SAB‐HLA‐Ab but without SAB‐detected donor‐specific Ab (SAB‐DSA) (HR: 4.91; 95% CI of 1.43–16.991; P = 0.012). ELISA was not sufficient to identify pretransplant immunized patients with an increased risk for graft loss. In immunized patients, graft loss was predominantly present in patients who received transplants with a mismatch on the HLA‐DR locus. In conclusion, even if our study is limited due to small sample size, the results show an increased risk for long‐term graft loss in patients with pretransplant SAB‐HLA, even in the absence of DSA. SAB‐HLA‐Ab‐positive patients, being negative in ELISA or CDC assay, might profit from a well‐HLA‐DR‐matched graft and intensified immunosuppression.     

Clinical impact of preformed donor‐specific denatured class I HLA antibodies after kidney transplantation

Class I single‐antigen flow beads (SAFB) carry native and denatured human leukocyte antigen (HLA) molecules. Using a cohort of 179 class I HLA‐sensitized kidney recipients, we described incidence and clinical relevance of preformed denatured HLA donor‐specific antibodies (DSA) using two different assays: an acid‐treated SAFB assay (anti‐dHLA DSA) and the iBeads assays (SAFB+/iBeads‐ DSA). Eighty‐five class I DSA were found in 67 patients (median mean fluorescence intensity [MFI] of 1729 [range 520–13 882]). Anti‐dHLA and SAFB+/iBeads‐ DSA represented 11% and 18% of class I DSA and were mainly low MFI DSA (500–1000 MFI). Concordance between these two assays was good (90%). None of the patients with only class I anti‐dHLA DSA or only SAFB+/iBeads‐ DSA developed acute clinical antibody‐mediated rejection in the first‐year post‐transplantation, and their five‐yr death‐censored graft survival was similar to that of patients without DSA. Moreover, all these patients displayed a negative current T‐cell flow cytometry cross‐match. Therefore, both anti‐dHLA DSA and SAFB+/iBeads‐ DSA appear irrelevant, which could explain the good outcome observed in some patients with preformed class I DSA.     

Both donor specific and non-donor specific HLA antibodies reduced in recipients post simultaneous liver/kidney transplant

It has been suggested that the liver allograft can protect the kidney allograft from antibody mediated rejection in simultaneous liver/kidney transplant (SLK) recipients by reducing preexisting donor specific antibodies (DSA) via adsorption of DSA by the liver allograft. Recently, the SLK allocation system was altered to provide a kidney safety net to those who do not recover native kidney function after liver transplant. However, the kidney transplant under the safety net creates a theoretical challenge for sensitized patients as the liver graft may not be able to adsorb human leukocyte antigen (HLA) antibodies against the kidney under the safety net because the liver and kidney grafts are from different donors and may carry different HLA antigens. This prompts us to examine levels of non-donor specific HLA antibodies in SLK recipients in our hospital. We found that levels of both DSA and non-DSA decreased post SLK transplant. The presence of preexisting DSA was also not associated with kidney graft survival and antibody mediated rejection in SLK recipients. Our results indicate that the liver transplant can reduce non-DSA, which may increase the pool of compatible kidneys offered under the safety net program for sensitized patients.     

Pretransplant identification of acute rejection risk following kidney transplantation

Lack of an accepted definition for ‘high immunological risk’ hampers individualization of immunosuppressive therapy after kidney transplantation. For recipient‐related risk factors for acute rejection, the most compelling evidence points to younger age and African American ethnicity. Recipient gender, body mass, previous transplantation, and concomitant infection or disease do not appear to be influential. Deceased donation now has only a minor effect on rejection risk, but older donor age remains a significant predictor. Conventional immunological markers (human leukocyte antigen [HLA] mismatching, pretransplant anti‐HLA alloantibodies, and panel reactive antibodies) are being reassessed in light of growing understanding about the role of donor‐specific antibodies (DSA). At the time of transplant, delayed graft function is one of the most clear‐cut risk factors for acute rejection. Extended cold ischemia time (≥24 h) may also play a contributory role. While it is not yet possible to establish conclusively the relative contribution of different risk factors for acute rejection after kidney transplantation, the available data point to variables that should be taken into account at the time of transplant. Together, these offer a realistic basis for planning an appropriate immunosuppression regimen in individual patients.     

High Mean Fluorescence Intensity Donor‐Specific Anti‐HLA Antibodies Associated With Chronic Rejection Postliver Transplant

In contrast to kidney transplantation where donor‐specific anti‐HLA antibodies (DSA) negatively impact graft survival, correlation of DSA with clinical outcomes in patients after orthotopic liver transplantation (OLT) has not been clearly established. We hypothesized that DSA are present in patients who develop chronic rejection after OLT. Prospectively collected serial serum samples on 39 primary OLT patients with biopsy‐proven chronic rejection and 39 comparator patients were blinded and analyzed for DSA using LABScreen^® single antigen beads test, where a 1000 mean fluorescence value was considered positive. In study patients, the median graft survival was 15 months, 74% received ≥ one retransplant, 20% remain alive and 87% had ≥ one episode of acute rejection. This is in contrast to comparator patients where 69% remain alive, and no patient needed retransplant or experienced rejection. Thirty‐six chronic rejection patients (92%) and 24 (61%) comparator patients had DSA (p = 0.003). Chronic rejection versus comparator patients had higher mean fluorescence intensity (MFI) DSA. Although a further study with larger numbers of patients is needed to identify clinically significant thresholds, there is an association of high‐MFI DSA with chronic rejection after OLT.     

Revisiting Traditional Risk Factors for Rejection and Graft Loss After Kidney Transplantation

Single‐antigen bead (SAB) testing permits reassessment of immunologic risk for kidney transplantation. Traditionally, high panel reactive antibody (PRA), retransplant and deceased donor (DD) grafts have been associated with increased risk. We hypothesized that this risk was likely mediated by (unrecognized) donor‐specific antibody (DSA). We grouped 587 kidney transplants using clinical history and single‐antigen bead (SAB) testing of day of transplant serum as (1) unsensitized; PRA = 0 (n = 178), (2) third‐party sensitized; no DSA (n = 363) or (3) donor sensitized; with DSA (n = 46), and studied rejection rates, death‐censored graft survival (DCGS) and risk factors for rejection. Antibody‐mediated rejection (AMR) rates were increased with DSA (p < 0.0001), but not with panel reactive antibody (PRA) in the absence of DSA. Cell‐mediated rejection (CMR) rates were increased with DSA (p < 0.005); with a trend to increased rates when PRA>0 in the absence of DSA (p = 0.08). Multivariate analyses showed risk factors for AMR were DSA, worse HLA matching, and female gender; for CMR: DSA, PRA>0 and worse HLA matching. AMR and CMR were associated with decreased DCGS. The presence of DSA is an important predictor of rejection risk, in contrast to traditional risk factors. Further development of immunosuppressive protocols will be facilitated by stratification of rejection risk by donor sensitization.