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Angiotensin II type-1 receptor antibody (AT1R-Ab) has been mooted as a potential effector of both acute and chronic antibody mediated rejection (AMR). A growing body of literature on the topic is now coming under scrutiny in the context of the evolving Banff AMR diagnostic classification system and refinement of recommendations for histocompatibility testing by the Sensitization in Transplantation Assessment of Risk (STAR) workgroup. This mini-review discusses the latest understanding of pathophysiological mechanisms, clinical evidence for the pathogenicity of AT1R-Ab, and methods of laboratory testing., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Martin, Willicombe and Roufosse.)

Introduction: The clinical relevance of preformed donor specific antibodies in the setting of a negative crossmatch (DSA + XM-) remains controversial. In this study we investigate the outcomes of patients with a DSA + XM- living donor (LDi) who proceeded with an HLA-incompatible (HLAi) transplant compared with those who waited for an HLA-compatible deceased donor (DDc)., Materials and Methods: We investigated 359 patients on the transplant waiting list who had at least one potential HLAi living donor, from which 203 DSA + XM- pairs were identified and outcomes analysed., Results: Out of 203 patients, 96 (47.3%) received a LD transplant: 52/96 (54.2%) a LDi, and 44/96 (45.8%) an alternative compatible LD. In addition, 107 patients out of 203(52.7%) waited for a DDc, of which 47(43.9%) were subsequently transplanted. Our adjusted analysis showed that the LDi transplantation did not offer a superior patient survival over waiting for a DDc transplant. For those transplanted, there was no difference in patient (p = 0.065) or death censored allograft survival (p = 0.37) between DDc and LDi recipients. However, there was a higher incidence of acute allograft rejection (p = 0.043) and antibody-mediated rejection (p = 0.005) in the LDi group. Having a high pre-transplant calculated reaction frequency and preformed DSA to both class I and class II antigens were associated with inferior outcomes in the LDi transplants., Conclusions: Given the lack of difference in allograft survival between LDi and DDc transplants, in the absence of an alternative compatible living donor, proceeding with a LDi should be supported despite a higher rejection risk, providing individual risk assessment and shared decision making is undertaken., Competing Interests: Declaration of competing interest The authors have no disclosures to declare related to this manuscript., (Copyright © 2024. Published by Elsevier B.V.)

Defining HLA mismatch at the molecular compared with the antigen level has been shown to be superior in predicting alloimmune responses, although data from across different patient populations are lacking. Using HLA-Matchmaker, HLA-EMMA and PIRCHE-II, this study reports on the association between molecular mismatch (MolMM) and de novo donor-specific antibody (dnDSA) in an ethnically diverse kidney transplant population receiving a steroid-sparing immunosuppression protocol. Of the 419 patients, 51 (12.2%) patients had dnDSA. De novo DSA were seen more frequently with males, primary transplants, patients receiving tacrolimus monotherapy, and unfavorably HLA-matched transplants. There was a strong correlation between MolMM load and antigen mismatch, although significant variation of MolMM load existed at each antigen mismatch. MolMM loads differed significantly by recipient ethnicity, although ethnicity alone was not associated with dnDSA. On multivariate analysis, increasing MolMM loads associated with dnDSA, whereas antigen mismatch did not. De novo DSA against 8 specific epitopes occurred at high frequency; of the 51 patients, 47 (92.1%) patients with dnDSA underwent a pretreatment biopsy, with 21 (44.7%) having evidence of alloimmune injury. MolMM has higher specificity than antigen mismatching at identifying recipients who are at low risk of dnDSA while receiving minimalist immunosuppression. Immunogenicity consideration is important, with more work needed on identification, especially across different ethnic groups., Competing Interests: Declaration of competing interest The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Pancreas transplant longevity is limited by immune rejection, which is diagnosed by graft biopsy using the Banff Classification. The histological criteria for antibody-mediated rejection (AMR) are poorly reproducible and inconsistently associated with outcome. We hypothesized that a 34-gene set associated with antibody-mediated rejection in other solid organ transplants could improve diagnosis in pancreas grafts. The AMR 34-gene set, comprising endothelial, natural killer cell and inflammatory genes, was quantified using the NanoString platform in 52 formalin-fixed, paraffin-embedded pancreas transplant biopsies from 41 patients: 15 with pure AMR or mixed rejection, 22 with T cell-mediated rejection/borderline and 15 without rejection. The AMR 34-gene set was significantly increased in pure AMR and mixed rejection (P = .001) vs no rejection. The gene set predicted histological AMR with an area under the receiver operating characteristic curve (ROC AUC) of 0.714 (P = .004). The AMR 34-gene set was the only biopsy feature significantly predictive of allograft failure in univariate analysis (P = .048). Adding gene expression to DSA and histology increased ROC AUC for the prediction of failure from 0.736 to 0.770, but this difference did not meet statistical significance. In conclusion, assessment of transcripts has the potential to improve diagnosis and outcome prediction in pancreas graft biopsies., (© 2020 The Authors. Clinical Transplantation published by John Wiley & Sons Ltd.)

Whether reexposure to mismatched HLA antigens (RMM) in the setting of a negative crossmatch is associated with increased immunological risk remains an area of uncertainty. This is due to evidence derived predominantly from registry data, which lacks comprehensive information on alloantibody and rejection. In this study, we analyze the impact of low-level preformed donor-specific antibodies (DSA) against an RMM on transplant outcomes. From 1988 consecutive renal transplant recipients, we analyzed 179 patients undergoing retransplantation, of whom 55 had a RMM. All patients were crossmatch negative and preformed DSA were detected by single antigen beads alone. Multivariate analysis revealed that patients with preformed DSA against an RMM were independently at risk of antibody-mediated rejection (HR 8.70 [3.42-22.10], P < .0001) and death-censored allograft loss (HR 3.08 [1.17-8.14], P = .023). In addition, prior transplant nephrectomy (HR 2.04 [1.00-4.17], P = .0495) was also associated with allograft failure, whereas receiving a retransplant that was matched at HLA class II was associated with a favorable outcome (HR 0.37 [0.14-0.99], P = .047). In the absence of preformed DSA, an RMM was not associated with de novo DSA development, rejection, or allograft loss. In conclusion, an RMM portends increased immunological risk only in the presence of a preformed DSA in patients undergoing retransplantation., (© 2019 The American Society of Transplantation and the American Society of Transplant Surgeons.)

Background: Severe peritubular capillary basement membrane multilayering (PTCBML) is part of the Banff definition of chronic antibody-mediated rejection. We retrospectively investigated whether assessment of the mean number of layers of basement membrane (BM) around peritubular capillaries (PTC) can be used in a cohort of patients with de novo donor-specific antibodies (dnDSA) as an early marker to predict long-term antibody-mediated injury., Methods: This is a retrospective cohort study with 151 electron microscopy samples from 54 patients with dnDSA, assessed at around 1 year after transplantation, for a mean number of BM layers around PTC and in serial biopsies. Graft survival and time to transplant glomerulopathy (TG) development were estimated in survival analyses., Results: We found that a mean PTCBML count greater than 2.5 layers assessed in a sample of 25 PTCs around 1 year after transplantation is indicative of the development of TG in patients with dnDSA (P = 0.001). In addition, in patients with serial biopsies available for electron microscopy analysis, we could distinguish 2 groups: patients with a mean PTCBML count of 2.5 or less on all biopsies, and patients who developed greater than 2.5 layers at any time after transplantation. The latter group reflected dnDSA patients at risk for TG development (P < 0.001). In patients with dnDSA, PTCBML score added significantly to the sensitivity and specificity of prediction of TG compared with microcirculation injury score alone., Conclusions: Our results highlight the potential value of assessing the mean number of BM in PTC for early prediction of progression to chronic antibody-mediated injury.

Introduction: Microarray studies have shown elevated transcript levels of endothelial and natural killer (NK) cell-associated genes during antibody-mediated rejection (AMR) of the renal allograft. This study aimed to assess the use of quantitative real-time polymerase chain reaction as an alternative to microarray analysis on a subset of these elevated genes., Methods: Thirty-nine renal transplant biopsies from patients with de novo donor-specific antibodies and eighteen 1-year surveillance biopsies with no histological evidence of rejection were analyzed for expression of 11 genes previously identified as elevated in AMR., Results: Expression levels of natural killer markers were correlated to microcirculation inflammation and graft outcomes to a greater extent than endothelial markers. Creating a predictive model reduced the number of gene transcripts to be assessed to 2, SH2D1b and MYBL1, resulting in 66.7% sensitivity and 89.7% specificity for graft loss., Discussion: This work demonstrates that elevated gene expression levels, proposed to be associated with AMR, can be detected by established quantitative real-time polymerase chain reaction technology, making transition to the clinical setting feasible. Transcript analysis provides additional diagnostic information to the classification schema for AMR diagnosis but it remains to be determined whether significant numbers of centres will validate transcript analysis in their laboratories and put such analysis into clinical use.

Corticosteroid use after transplantation is associated with an increased incidence of cardiovascular events and death. Cerebrovascular disease is a common cause of morbidity and mortality post-renal transplantation; however, a dedicated analysis of cerebrovascular disease in recipients of a steroid sparing protocol has not been reported. The aim of this study was to examine the incidence, risk factors, and outcomes of CVA in transplant recipients receiving a steroid sparing protocol. We retrospectively analyzed 1237 patients who received a kidney alone or a simultaneous pancreas and kidney (SPK) transplant. Fifty-six of 1237 (4.53%) patients had a CVA post-transplant. All-cause mortality was significantly higher in the CVA group compared with the non-CVA group, OR: 3.4 (1.7-7.0), p < 0.001. Factors found to be associated with increased risk of CVA by multivariate analysis were older age, HR: 1.07 (1.04-1.09), p < 0.001; diabetes at the time of transplantation, HR: 2.83 (1.42-5.64), p = 0.003; corticosteroid use pre-transplant, HR: 3.27 (1.29-8.27), p = 0.013 and recipients of a SPK, HR: 4.03 (1.85-8.79), p < 0.001. This study has identified subgroups of patients who are at increased risk of CVA post-transplant in patients otherwise receiving a steroid sparing immunosuppression protocol., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Mixed rejection in kidney transplantation consists of histologic and/or serological evidence of both cellular and humoral components. As it is not confined to a distinct category in the Banff classification, how to best manage these patients is not clear. The aim of this study was to determine the incidence and outcome of morphological T-cell-mediated rejection (TCMR) with a humoral component, defined as the presence of either DSA or C4d, compared with the outcome of pure TCMR., Methods: We retrospectively studied 922 consecutive renal transplant recipients and analyzed patients with TCMR according to the evidence of a humoral component., Results: A total of 147 cases of morphological TCMR were analyzed. Of these, 92 (62.6%) had "pure" TCMR and 55 (37.4%) had "mixed" TCMR on the index biopsy. On univariant analysis, diffuse C4d (odds ratio [OR]=10.9, 95% confidence interval [CI]=1.8-66.9, P=0.01) and DSA positivity at the time of index biopsy (OR=2.8, 95% CI=1.2-6.6, P=0.02) were associated with allograft loss, whereas arteritis (OR=0.5, 95% CI=0.2-1.2, P=0.11) and glomerulitis (OR=0.9, 95% CI=0.4-2.1, P=0.8) were not. Arteritis was associated with subsequent antibody-mediated rejection (OR=4.9, 95% CI=1.1-20.8, P=0.03), and glomerulitis was associated with the development of transplant glomerulopathy (OR=10.7, 95% CI=3.1-37.1, P<0.01). On the multivariate analysis, only patients with C4d and DSA were at risk of graft failure (OR=4.9, 95% CI=2.0-12.0, P<0.01) in the medium term., Conclusion: TCMR with a humoral component has a worse prognosis when compared with pure TCMR. As such, it is important to test for alloantibody in cases of morphological TCMR to optimize patient management. Such cases might benefit from more aggressive immunotherapy.

A kidney transplant recipient developed chronic antibody-mediated rejection (ABMR) with clinically significant transplant glomerulopathy while under careful clinical monitoring. The patient developed a de novo donor-specific antibody (DSA) posttransplantation, and a protocol renal biopsy showed C4d deposition with no histological evidence of rejection. Subsequently he developed peritubular capillary basement membrane multilayering, with negative C4d and DSA. Finally, he developed proteinuria and transplant glomerulopathy, with reappearance of DSA and C4d. Despite having a de novo antibody and progressive antibody-mediated damage, this patient under close histological and serological surveillance did not fulfill Banff criteria for acute or chronic ABMR until his disease was advanced. This case illustrates the limitations of current Banff criteria in this setting, due to the fluctuating nature of DSA and C4d staining.

BACKGROUND.: Donor-specific anti-HLA antibodies (DSA) are a major cause of alloimmune injury. Transplant recipients with negative complement-dependent cytotoxic crossmatch (CDC-XM) and donor cell-based flow cytometric crossmatch (flow-XM) but low level DSA (i.e., by Luminex) have worse outcomes compared with nonsensitized patients. The aim of this study was to establish whether complement-activating ability in this low-level DSA, present before transplantation, as determined by this technique is important in dictating pathogenicity. METHODS.: We retrospectively studied 52 patients with preformed DSA detected by single-antigen flow cytometric fluorescent beads (SAFBs). Patients were transplanted using a steroid-sparing regimen consisting of alemtuzumab induction, 1 week of corticosteroids and tacrolimus monotherapy.Fifteen (29%) of 52 patients experienced antibody-mediated rejection (AMR), whereas 37 (71%) patients did not. There were no demographic differences between patients with AMR and those without. Pretransplant sera were retested using a modified (SAFB) assay, which detects the presence of the complement fragment C4d as a result of DSA-induced complement activation. RESULTS.: C4d+DSA were detected in 10 (19%) of 52 patients. Biopsy-proven AMR occurred in 7 (70%) of the 10 patients with C4d+DSA and in 8 (19%) of 42 patients with C4d-DSA. AMR-free survival was worse in patients with C4d+DSA (P<0.001). CONCLUSIONS.: The ability of preformed, low-level, DSA to trigger C4d fixation in vitro in patients with negative conventional crossmatch tests is predictive for AMR. C4d SAFB is potentially a powerful tool for risk stratification prior to transplantation and may allow identification of unacceptable donor antigens, or patients who may require enhanced immunosuppression.

Background: The importance of human leukocyte antigen (HLA) matching in renal transplantation is well recognized, with HLA-DR compatibility having the greatest influence. De novo DQ donor-specific antibodies (DSAbs) are the predominant HLA class II DSAb after transplantation. The aim of this study was to establish the incidence and outcomes after the development of DQ DSAbs along with the impact of class II HLA mismatch on their development., Methods: We retrospectively analyzed 505 patients who received a renal-alone transplant between 2005 and 2010. We excluded patients who received an ABO- and HLA-incompatible allograft, which we defined as those with a positive crossmatch or preformed DSAbs detected by single-antigen beads only., Results: Of 505 patients, 92 (18.2%) developed DSAbs, with 50 (54.3%) of these 92 patients having DQ DSAbs. Patients who developed DQ DSAbs were at significant risk for antibody-mediated rejection, transplant glomerulopathy, and allograft loss (P<0.0001). Of 505 patients, 108 (21.4%) were matched at both the DR and DQ loci, 284 (56.2%) were mismatched at both loci, 38 (7.5%) were matched at DR alone, and 75 (14.9%) were matched at DQ alone. Patients mismatched at both DR and DQ were at risk for developing class II DSAbs when compared with those mismatched at either DR or DQ alone, P=0.001, and were at risk for antibody-mediated rejection, P=0.001., Conclusions: DQ DSAbs are associated with inferior allograft outcomes. This study shows the importance of establishing the DQ match before transplantation to define immunologic risk.

Background: Antibody-mediated rejection (AMR) is associated with allograft loss. Identification of factors associated with poor outcome has not been extensively studied., Methods: We retrospectively studied 469 patients who received a negative crossmatch renal transplant with alemtuzumab induction. Forty-eight of 469 (10.2%) patients were treated for AMR. Thirty of 48 (62.5%) of the cases fulfilled the Banff criteria for definite AMR, whereas 18 of 48 (37.5%) were categorized as suspicious for AMR (tissue injury with C4d staining or donor-specific antibodies [DSAbs]). Sensitization, high human leukocyte antigen, and -DR mismatch were risk factors for the development of AMR (P = 0.0016, 0.001, and 0.012, respectively)., Results: Allograft survival was inferior in the AMR group (70.2%) compared with the nonrejector group (97.0%) (P<0.001). Forty-two of 48 (87.5%) of patients with acute AMR had DSAbs. Patients with CII DSAbs at the time of AMR, whether alone or in combination with CI DSAbs had the worst allograft survival (P = 0.014). Both the mean cumulative and immunodominant mean fluorescence index were higher in those patients who subsequently lost their grafts (P<0.001). Patients with diffuse C4d staining had inferior allograft survival than those with focal C4d or no staining (P = 0.02). There was no significant difference in survival by histological grade but a trend to inferior outcomes in those with vascular involvement (P = 0.06). Those patients who met the full Banff criteria had worse survival than those with suspicion for AMR only (P = 0.04)., Conclusion: This study identifies patients at risk of graft failure from AMR. These patients may benefit from newer therapeutic strategies including the use of eculizumab or bortezomib.

It has been shown that low-level preformed donor-specific antibodies (DSAbs) detected by luminex beads in the setting of a negative CDC and flow cytometry crossmatch (CDC/FCXM) are associated with inferior allograft outcomes. The relevance of preformed DSAbs in patients receiving alemtuzumab induction and tacrolimus monotherapy has not been studied. Four hundred and eighty renal transplant recipients with a negative CDC/FCXM had their pretransplant sera retrospectively screened for DSAbs. 45/480 (9.4%) of patients were found to have preformed DSAbs. Females and patients receiving regrafts were more likely to have a DSAb (p = 0.008 and p < 0.0001, respectively). Patients with DSAbs had inferior allograft survival (p = 0.047), increased incidence of antibody-mediated rejection (p < 0.0001) and inferior allograft function at 6 months posttransplant (p = 0.017). Patients with HLA class I DSAb (alone or in combination with a Class II DSAb) with high mean fluorescence intensities (MFIs) were at highest risk. We conclude that patients with preformed DSAb are at high risk of adverse outcomes when receiving a minimal immunosuppressive regime incorporating alemtuzumab induction. Patients found to have a preformed DSAb despite a negative crossmatch might benefit from augmented immunosuppression., (©2011 The Authors Journal compilation©2011 The American Society of Transplantation and the American Society of Transplant Surgeons.)