Use of complement binding assays to assess the efficacy of antibody mediated rejection therapy and prediction of graft survival in kidney transplantation.

The Luminex® single antigen bead assay (SAB) is the method of choice for monitoring the treatment for antibody-mediated rejection (AMR). A ⩾50% reduction of the dominant donor-specific antibody (IgG-DSA) mean fluorescence intensity (MFI) has been associated with improved kidney allograft survival, and C1q-fixing DSA activity is associated with poor outcomes in patients with AMR. We aimed to investigate if C1q-DSA can be used as a reliable predictor of response to therapy and allograft survival in patients with biopsy-proven AMR. We tested pre- and post-treatment sera of 30 kidney transplant patients receiving plasmapheresis and low-dose IVIG for biopsy-proven AMR. IgG-DSA and C1q-DSA MFI were measured and correlated with graft loss or survival. Patients were classified as nonresponders (NR) when treatment resulted in <50% reduction in MFI of IgG-DSA and/or C1q-DSA was detectable following therapy. Differences in the percentage of patients deemed NR depended upon the end-point criterion (73% by reduction in IgG-DSA MFI vs. 50% by persistent C1q-DSA activity). None of the seven patients with <50% reduction of IgG-DSA but non-detectable C1q-DSA-fixing activity after therapy experienced graft loss, suggesting that C1q-DSA activity may better correlate with response. Reduction of C1q-DSA activity predicted graft survival better than IgG-DSA in the univariate Cox analysis (20.1% vs. 5.9% in NR; log-rank P-value=0.0147). A rapid reduction of DSA concentration below the threshold required for complement activation is associated with better graft survival, and C1q-DSA is a better predictor of outcomes than IgG-DSA MFI reduction.

Ramon DS ，Huang Y ，Zhao L ，Rendulic T ，Park JM ，Sung RS ，Samaniego M ... -  《-》

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.

Malheiro J ，Tafulo S ，Dias L ，Martins S ，Fonseca I ，Beirão I ，Castro-Henriques A ，Cabrita A ... -  《-》

Clinical relevance of pretransplant anti-HLA donor-specific antibodies: does C1q-fixation matter?

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

Crespo M ，Torio A ，Mas V ，Redondo D ，Pérez-Sáez MJ ，Mir M ，Faura A ，Guerra R ，Montes-Ares O ，Checa MD ，Pascual J ... -  《-》

Detection of Complement-binding Donor-specific Antibodies, Not IgG-antibody Strength Nor C4d Status, at Antibody-mediated Rejection Diagnosis Is an Independent Predictor of Kidney Graft Failure.

Malheiro J ，Santos S ，Tafulo S ，Dias L ，Martins S ，Fonseca I ，Almeida M ，Pedroso S ，Beirão I ，Castro-Henriques A ，Cabrita A ... -  《-》

C1q Binding Activity of De Novo Donor-specific HLA Antibodies in Renal Transplant Recipients With and Without Antibody-mediated Rejection.

Yell M ，Muth BL ，Kaufman DB ，Djamali A ，Ellis TM ... -  《-》