C1q-binding Donor-specific Antibodies Research Articles

Efficacy of Double Membrane Filtration Immunoadsorption in Severe C1q-Binding Donor-Specific Antibody-Positive Acute Humoral Kidney Allograft Rejection: A Case Series

Introduction: Acute antibody-mediated rejection (ABMR) is an important threat to renal allograft survival in the early transplant period and the major single cause of graft loss in the first postoperative year. Semi-selective immunoadsorption (IA) remains one of the commonly applied treatments in ABMR, reducing allo-reactive antibody load. Adding double filtration plasmapheresis (DFPP) to IA might enhance therapeutic efficacy by also addressing innate humoral effectors like complement factors. Methods: Four patients with ABMR were treated with DFPP + IA. Clinical, histological, and immunological data and adverse events were retrospectively collected. Results: Here we present four high-risk treatment-refractory ABMR cases with C1q-binding donor-specific antibodies and histology of humoral rejection under treatment with DFPP + IA. While the earlier cases (within the first year after transplantation) showed marked reduction in ABMR severity and improvement of kidney function, the later cases did not respond accordingly. Late ABMR patient 1 stabilized, whereas late ABMR patient 2 did not respond to treatment. Conclusions: Our data support the consideration of DFPP + IA as a rescue treatment option in early, severe, high-risk ABMR cases in which other treatments failed.

Can Heart Allografts Protect Simultaneous Kidney Allografts from Antibody Injury?

<h3>Purpose</h3> Pre-formed donor specific antibodies (DSA) are associated with antibody mediated rejection (AMR) and graft loss in kidney transplants. However, simultaneous liver/kidney transplants show a lower risk for DSA mediated AMR in kidney allograft, likely due to absorbance of DSAs by the liver allograft. The goal of this study is to determine if heart allografts can protect subsequent kidney grafts from antibody mediated injury. <h3>Methods</h3> 93 patients were transplanted with combined heart and kidney allografts between 2016 and 2020 at our center. The median time (interquartile range [IQR]) of post-transplant follow up is 883 days (459-1322). Treatment for patients transplanted across DSA included intravenous immune globulin, obinutuzumab, and eculizumab. <h3>Results</h3> 12 of 93 recipients had pre-formed DSA, with 3 recipients having strong pre-formed DSA (MFI>10,000); 5 recipients having moderate DSA (MFI >5,000); 4 recipients having weak DSA (MFI>2,500). Survival was not different between recipients with preformed DSA and recipients without preformed DSA (p=0.436) (Fig. 1). Of these 12 patients with pre-formed DSA, 4 patients had positive flow crossmatches and were treated with intravenous immune globulin. Notably, one of these 4 patients also had a positive CDC crossmatch with pre-formed C1q-binding DSA and was treated with obinutuzumab and eculizumab in addition to intravenous immune globulin. All 4 patients had stable renal and cardiac function at the end of the follow up. DSA in 3 of these 4 patients including the patient with positive CDC crossmatch, became negative during the follow up (Fig. 2). <h3>Conclusion</h3> Levels of DSA can decrease post heart/kidney transplant, suggesting the heart/kidney transplant may modulate antibody response. Our study indicates that the kidney can be transplanted across strong DSA in heart/kidney combined transplant with acceptable outcomes.

Successful Eradication of De Novo C1q-Binding Donor-Specific Antibodies with Rituximab Monotherapy

<h3>Introduction</h3> Antibody-mediated rejection (AMR) is an increasingly recognized cause of lung transplant allograft failure. Treatment of AMR involves combination therapy that is often poorly tolerated or unsuccessful with regimens involving the combination of intravenous immunoglobulins, plasmapheresis, and proteasome inhibitors, complement, or CD20 therapy. The development of DSAs alone, specifically complement activating C1q-binding DSAs, has been identified as an independent risk factor for solid organ transplant allograft dysfunction. Previous studies have examined the efficacy of combination therapy involving the anti-CD20 antibody rituximab to preemptively eliminate DSAs. Here we report on a case of successful eradication of de novo C1q-binding DSAs in a lung transplant recipient using rituximab. <h3>Case Report</h3> Our patient underwent double-lung transplantation for idiopathic pulmonary fibrosis in August 2019. His post-transplant course was notable for multiple episodes of acute cellular rejection (ACR) requiring burst-dose corticosteroids. DSA titers were monitored every three months post-transplant. At six months, de novo DSAs were detected (DQ7 with DQA1*05) at a mean fluorescence intensity (MFI) of 3623 (low-moderate) (Figure 1). These subsequently rose to an MFI of 11281 (strong) with development of C1q positivity that peaked at an MFI of 15038. Given his frequent episodes of ACR, the strong C1q positivity, and concerns regarding his ability to tolerate therapy for potential future AMR, he was preemptively treated with a single infusion of rituximab (375 mg per meter-squared body surface area). Follow-up DSA titers demonstrated near-total elimination of the C1q component (MFI 403). The patient tolerated the treatment without issue and continues to demonstrate improvement in his allograft function. <h3>Summary</h3> Rituximab monotherapy can be considered preemptively in patients with C1q-binding DSAs that may not tolerate traditional treatment of antibody-mediated rejection.

C1q-binding DSA and allograft outcomes in pediatric kidney transplant recipients.

Donor-specific antibody (DSA) is an independent risk factor for antibody-mediated rejection (ABMR) and graft loss. The C1q assay differentiates complement from non-complement-binding DSA and C1q-binding DSA may lead to poor allograft survival. Our aim was to characterize the type of DSA seen in pediatric kidney transplant recipients and to determine whether complement binding DSA was associated with inferior graft survival.This was a single-center retrospective study of 48 children who were transplanted between 2009 and 2016. DSA were monitored using Luminex single antigen beads. A negative crossmatch was required to proceed with transplantation. The median follow-up time was 4.9 (3.4, 7.9) years. The median age was 12 (5.7, 15.4) years. DSA developed in 27/48 (56.3%), while C1q-binding DSA developed in 17/27 (63%). There were no significant differences between DSA negative, C1q-binding DSA, and C1q negative DSA, with regard to the number of HLA-ABDR (P = .09) or HLA-DQ mismatches alone (P = .16). For both C1q negative and C1q-binding DSA, DQ was the most common target of the DSA (19/27; 70.4%). C1q-binding DSA was associated with a significantly higher frequency of biopsy proven rejection (76.5%) when compared to C1q negative (10%) and DSA negative (14.3%); P = .001. Graft loss was seen in 6 (12.5%), all of whom had C1q-binding DSA (P = .004). C1q-binding DSA was most commonly directed to DQ antigens. C1q-binding DSA was associated with increased rejection and graft loss. Monitoring for C1q-binding DSA may risk stratify recipients and guide physician management.

Association between post-transplant donor-specific antibodies and recipient outcomes in simultaneous liver-kidney transplant recipients: single-center, cohort study.

There is a dearth of published data regarding the presence of post-transplant donor-specific antibodies (DSA), especially C1q-binding DSA (C1q+DSA), and patient and kidney allograft outcomes in simultaneous liver-kidney transplant (SLKT) recipients. We conducted a retrospective cohort study consisted of 85 consecutive SLKT patients between 2009 and 2018 in our center. Associations between presence of post-transplant DSA, including persistent and/or newly developed DSA and C1q+DSA, and all-cause mortality and the composite outcome of mortality, allograft kidney loss, and antibody-mediated rejection were examined using unadjusted and age and sex-adjusted Cox proportional hazards and time-dependent regression models. The mean age at SLKT was 56years and 60% of the patients were male. Twelve patients (14%) had post-transplant DSA and seven patients (8%) had C1q+DSA. The presence of post-transplant DSA was significantly associated with increased risk of mortality (unadjusted model: Hazard Ratio (HR)=2.72, 95% confidence interval (CI): 1.06-6.98 and adjusted model: HR=3.20, 95% CI: 1.11-9.22) and the composite outcome (unadjusted model: HR=3.18, 95% CI: 1.31-7.68 and adjusted model: HR=3.93, 95% CI: 1.39-11.10). There was also higher risk for outcomes in recipients with C1q+DSA compared the ones without C1q+DSA. Post-transplant DSA is significantly associated with worse patient and kidney allograft outcomes in SLKT. Further prospective and large cohort studies are warranted to better assess these associations.

C1q-binding donor-specific antibody assays help define risk and prognosis in antibody-mediated rejection

Antibody-mediated rejection represents the first cause of graft loss in renal transplant recipients, and it is imperative to identify appropriate tools to enable risk stratification of such patients. Lately, the usefulness of measuring complement-binding anti-human leukocyte antigen (HLA) donor-specific antibodies (DSAs) in renal transplantation has been intensely debated. While the jury is still out, recent data suggest that monitoring complement-binding DSAs may help to recognize high-risk patients and possibly trigger more effective interventions in selected patients.

P037 Pre-transplant HLA DP10 donor specific antibody of unknown significance in heart transplant a case study

There is minimal data in the literature on the impact of pre-formed HLA DPB1 Donor Specific Antibodies in heart transplant patients. Accurately assessing these antibodies and the risk they pose would hopefully broaden the donor pool available to this group of patients. We have reviewed a case of heart transplantation across strong C1q binding donor specific antibody (DSA) to the HLA DP epitopes 84DEAV and 96K2. A 64y/o female with a history of breast cancer (1997), coronary artery disease, hypertension, hyperlipidemia (2002), presented with congestive heart failure. Sensitization history includes two children but no transfusions prior to transplant evaluation. Her initial HLA antibody results were reported as 0% cPRA for Class I and Class II (Luminex Single Antigen). There were HLA-DP antibodies present below the reporting cutoff ( 10,000 MFI). Antibody testing was done 10 days post LVAD implantation. Unfortunately, her cPRA levels increased dramatically (to 70% Class I and 48% Class II). The Class II antibodies were largely HLA-DP, likely to the 84DEAV and 96 K epitopes. Epitope analysis was initially performed using the HLA-DPB Compatability Wizard. The patient received a heart offer. Virtual crossmatch revealed a single DSA (Anti-DP10 > 20,000 MFI). A prospective CDC crossmatch was performed and was negative. The patient’s auto crossmatch was also negative. The patient was transplanted with this donor. A retrospective flow crossmatch was performed with pronase treated cells. It was T-cell negative, B-cell positive. Due to the positive flow crossmatch, the heart team performed one session of PP/IVIG on POD 1. This case provides insight to the role of high level C1q binding pre-formed donor specific HLA-DPB antibody, where the antibody is not confounded by additional DSA to other loci. It supports the concept that pre-existing HLA-DP antibodies may not represent a significant barrier to transplantation.

Prognostic Value of the Persistence of C1q-Binding Anti-HLA Antibodies in Acute Antibody-Mediated Rejection in Kidney Transplantation.

The differential pathogenicity of anti-HLA donor-specific antibodies (DSAs) is not fully understood. The presence of complement-binding DSAs helps in better defining the prognosis of acute antibody-mediated rejection (ABMR). The evolution of these antibodies after the treatment of ABMR is unknown. We included patients from the French multicenter RITUX ERAH study diagnosed with acute ABMR within the first year of renal transplantation, with circulating anti-HLA DSAs and treated randomly by rituximab or placebo (and intravenous immunoglobulins, plasma exchange). We centrally analyzed serum samples at the time of ABMR, 3 and 6 months after ABMR, with anti-HLA DSAs specificities and C1q-binding capacity assessment. Twenty-five patients were included: 68% had C1q-binding DSAs at the time of ABMR. The presence of C1q-binding DSAs was associated with a poorer evolution of chronic glomerulopathy at 6 months (P = 0.036). The persistence of C1q-binding DSAs at 3 and/or 6 months after ABMR was associated with more severe chronic glomerulopathy (P = 0.006), greater C4d score deposition score at 6 months after ABMR (P = 0.008), and graft loss 5 years after ABMR (P = 0.029). C1q-binding capacity was associated with the DSA MFI but 5 C1q-binding DSAs in 4 patients had low MFI values without a prozone effect. The presence and persistence of anti-HLA C1q-binding DSAs after ABMR is a detrimental marker, leading to transplant glomerulopathy and graft loss. Assessment of the complement-binding capacities of DSAs could help decide treatment intensification.

Complement-fixing donor-specific anti-HLA antibodies and kidney allograft failure

Detection of donor-specific antibodies (DSA) has improved the risk classification and post-transplant evaluation of kidney recipients. Moreover, assessment of DSA C1q-binding ability has been shown to improve the individual risk classification of transplant patients for allograft loss, especially when detected after transplantation. The aim of this study was to evaluate the additional clinical impact of C1q-binding DSA detection in a population that was extensively monitored for DSA and MFI alterations. Forty-two kidney allograft recipients were followed-up at multiple time points for up to 5 years after transplantation for the presence of anti-HLA DSA-IgG total. The samples that were positive for these antibodies were retrospectively tested for the presence of complement-binding antibodies. Overall, 24 patients presented DSA, 29% (7) of which also produced complement-binding DSA. Compared to patients with non-C1q-binding DSA and non-sensitized patients, patients with C1q-binding DSA after transplantation had the lowest allograft survival rate at 5 years (p = 0.042) and showed a lower estimated glomerular filtration rate (based on the Modification of Diet in Renal Disease formula) during the post-transplant follow-up period (p = 0.01). Thus, post-transplant monitoring for complement-binding DSA is a useful tool for predicting individuals most at risk for allograft failure, and might also be beneficial for evaluation of immunosuppression regimens.

Complement (C1q) Binding De Novo Donor-Specific Antibodies and Cardiac-Allograft Vasculopathy in Pediatric Heart Transplant Recipients.

We hypothesized C1q binding de novo donor-specific antibody (DSA) after heart transplant (HT) is a higher risk for development of coronary artery vasculopathy (CAV) in children. A retrospective analysis of 127 pediatric HT recipients transplanted between January 2005 and December 2014 was used to determine complement (C1q)-binding de novo DSA on the outcomes of HT and the ability of the C1q assay to predict CAV development. Of 127 patients, 59 (46.4%) developed de novo DSA, 37 of those had C1q+ DSA. There was no difference in baseline characteristics except patients who developed C1q+ DSA more often received a donor heart from a female compared with C1q- DSA group (P = 0.034). The DSA median fluorescent intensity (MFI) value of 7000 or greater had 80% sensitivity and 80% specificity (C statistics 0.89, P <0.05) for predicting positive C1q binding. Multivariate analyses identified C1q binding DSA as an independent risk for CAV with a hazard ratio (HR) of 3.25 (95% confidence interval [CI], 1.33-7.93; P = 0.0095). In multivariable Cox proportional hazard models, the covariates associated with graft loss included: C1q+ DSA (HR, 3.2; 95% CI, 1.34-7.86; P < 0.009), pre-HT renal insufficiency (HR, 11.3; 95% CI, 3.71-34.29; P < 0.0001), and pre-HT ventilator support (HR, 3.3; 95% CI, 1.39-7.81; P = 0.007). The DSA strength in MFI correlates with positive C1q-binding activity and hence functional capabilities of DSA. Close monitoring of DSA strength in MFI and function (C1q assay) may be useful for identifying pediatric HT recipient at risk for development of CAV.

Donor-Specific Antibodies in Kidney Transplant Recipients.

Donor-specific antibodies have become an established biomarker predicting antibody-mediated rejection. Antibody-mediated rejection is the leading cause of graft loss after kidney transplant. There are several phenotypes of antibody-mediated rejection along post-transplant course that are determined by the timing and extent of humoral response and the various characteristics of donor-specific antibodies, such as antigen classes, specificity, antibody strength, IgG subclasses, and complement binding capacity. Preformed donor-specific antibodies in sensitized patients can trigger hyperacute rejection, accelerated acute rejection, and early acute antibody-mediated rejection. De novo donor-specific antibodies are associated with late acute antibody-mediated rejection, chronic antibody-mediated rejection, and transplant glomerulopathy. The pathogeneses of antibody-mediated rejection include not only complement-dependent cytotoxicity, but also complement-independent pathways of antibody-mediated cellular cytotoxicity and direct endothelial activation and proliferation. The novel assay for complement binding capacity has improved our ability to predict antibody-mediated rejection phenotypes. C1q binding donor-specific antibodies are closely associated with acute antibody-mediated rejection, more severe graft injuries, and early graft failure, whereas C1q nonbinding donor-specific antibodies correlate with subclinical or chronic antibody-mediated rejection and late graft loss. IgG subclasses have various abilities to activate complement and recruit effector cells through the Fc receptor. Complement binding IgG3 donor-specific antibodies are frequently associated with acute antibody-mediated rejection and severe graft injury, whereas noncomplement binding IgG4 donor-specific antibodies are more correlated with subclinical or chronic antibody-mediated rejection and transplant glomerulopathy. Our in-depth knowledge of complex characteristics of donor-specific antibodies can stratify the patient's immunologic risk, can predict distinct phenotypes of antibody-mediated rejection, and hopefully, will guide our clinical practice to improve the transplant outcomes.

Tac-MMF Versus CsA-MMF/CsA-AZA–Based Regimens in Development of De Novo Complement-Binding Anti-HLA Antibodies After Kidney Transplantation

BackgroundImmunosuppressive regimens with tacrolimus or cyclosporine A (CsA) were compared for graft-related outcomes in conjunction with complement-binding de novo donor-specific antibodies (DSAs). MethodsNon-sensitized adult patients without rejection episodes within 3 months after transplantation were screened for the presence of de novo DSAs and C1q binding. Clinical and biopsy data were retrospectively obtained. ResultsThe analysis included 118 patients (68 tacrolimus, 50 CsA), with mean age and follow-up of 36.1 ± 11.4 and 7.2 ± 4.8 years, respectively. As compared with tacrolimus, the CsA group had higher rates of both class II DSAs and C1q-binding DSAs (20% vs 4.4%, P = .008, and 18% vs 0%, P = .003, respectively). Rates of chronic antibody-mediated rejection (cAMR), proteinuria >500 mg/g, and levels of creatinine both at last visits were also higher in the CsA group (20% vs 0%, P = .002, 30% vs 5.9%, P = .005, 1.67 ± 1.31 vs 1.18 ± 0.45 mg/dL, P = .019, respectively).Class II DSAs and C1q-binding class II DSAs were significantly correlated with the clinical outcomes (creatinine levels, proteinuria, and cAMR). ConclusionsCompared with tacrolimus, CsA appears to pose a higher risk for the development of de novo anti-HLA antibodies with C1q-binding properties and, consequently, adverse graft-related outcomes.

C1q binding is not an independent risk factor for kidney allograft loss after an acute antibody-mediated rejection episode: a retrospective cohort study.

After kidney transplantation, C4d is an incomplete marker of acute antibody-mediated rejection (AMR) and C1q-binding donor-specific antibodies (DSA) have been associated with allograft survival. However, the impact on allograft survival of C1q+ DSA after clinical AMR has not been studied yet. We analysed retrospectively in clinical AMR C4d staining and C1q-binding impact on allograft survival. We compared clinical, histological and serological features of C4d- and C4d+ AMR, C1q+ and C1q- DSA AMR and analysed C4d and C1q-binding impact on allograft survival. Among 500 for-cause kidney allograft biopsies, 48 fulfilled AMR criteria. C4d+ AMR [N=18 (37.5%)] have significantly higher number class I DSA (P=0.02), higher microvascular score (P=0.02) and more transplant glomerulopathy (P=0.04). C1q+ AMR [N=20 (44%)] presented with significantly more class I and class II DSA (P=0.005 and 0.04) and C4d+ staining (P=0.01). Graft losses were significantly higher in the C4d+ group (P=0.04) but similar in C1q groups. C4d+ but not C1q+ binding was an independent risk factor for graft loss [HR=2.65; (1.11-6.34); P=0.028]. In our cohort of clinical AMR, C4d+ staining but not C1q+ binding is an independent risk factor for graft loss. Allograft loss and patient survival were similar in C1q+ and C1q- AMR.

Assignment of C1q-binding HLA antibodies as unacceptable HLA antigens avoids positive CDC-crossmatches prior to transplantation of deceased donor organs

Soon, a virtual crossmatch shall replace the complement-dependent cytotoxicity (CDC) allocation crossmatch in the Eurotransplant region. To prevent positive CDC-crossmatches in the recipient centre, careful definition of unacceptable antigens is necessary. For highly sensitized patients, this is difficult by CDC alone. Assignment of all antibodies detected by sensitive assays, however, could prevent organ allocation. To assess the usefulness of the Luminex C1q-assay to prevent positive CDC-crossmatches, all CDC-crossmatches performed prior to deceased kidney transplantation in a 16-month-period were reviewed. Sera causing positive crossmatches were investigated by the C1q-assay. 31 out of 1432 crossmatches (2.2%) were positive. Sera involved in 26 positive crossmatches were available. C1q-binding donor-specific antibodies were detected in 19 sera (73.1%). The other sera were from recipients without any HLA antibodies detectable by CDC or common solid phase assays. Three patients had known Non-HLA antibodies causing positive CDC-results. Four crossmatches were only weak positive. Therefore, avoidance of donors with HLA antigens against whom C1q-binding antibodies were detected would have prevented all positive crossmatches due to HLA antibodies. Provided that all HLA specificities against which antibodies are detected by the Luminex C1q-assay are considered as unacceptable antigens, CDC-crossmatches prior to transplantation might safely be omitted in many patients. They should be maintained in highly immunized patients, however, for whom assignment of all C1q-positive antibodies as unacceptable antigens could lead to a significant delay or even prevention of transplantation.

De Novo Anti-HLA DSA Characteristics and Subclinical Antibody-Mediated Kidney Allograft Injury.

It is unclear whether all donor-specific antibodies (DSA) can cause chronic antibody-mediated rejection (AMR). Subclinical stage before manifestation of renal dysfunction may be a critical period for reversing AMR. The aim of our study was to identify factors related to the development of subclinical AMR and to clarify the characteristics of de novo DSA. Eight hundred ninety-nine renal transplants were screened for HLA antibody. De novo DSA were detected in 95 patients. Forty-three patients without renal dysfunction who underwent renal biopsies were enrolled in this study. Eighteen patients (41.9%) were diagnosed with biopsy-proven subclinical AMR and treated with plasmapheresis and rituximab-based therapy, whereas 25 showed no findings of AMR. Significant subclinical AMR-related factors were younger recipients, history of acute T cell-mediated rejection and DSA class II, especially DR-associated DSA. Mean fluorescence intensity (MFI) values of DR-DSA were significantly higher, whereas DQ-DSA was not different between subclinical AMR and no AMR. The ΔMFI (>50%), DSA-MFI values greater than 3000, and C1q binding DSA were also significant subclinical AMR-related factors (P < 0.05). Among 18 patients treated for subclinical AMR, 8 patients (44.4%) obtained over 50% reduction of DSA-MFI and/or improvement or no deterioration of pathological findings. In contrast, 25 patients without subclinical AMR did not show renal dysfunction clinically. Moreover, all of the 8 patients with rebiopsy after 2 years continued to demonstrate no AMR. About 40% of patients with de novo DSA demonstrated biopsy-proven subclinical AMR, leading to progressive graft injury. To validate the intervention and treatment for de novo DSA-positive patients without renal dysfunction, further study is necessary.

Association of C1q Binding Status With De Novo HLA Antibody Clinical Features and Allograft Function in Kidney Transplantation Patients During Eight Years of Dynamic Follow-up

C1q-binding donor-specific antibody (DSA) is detrimental to transplanted kidney function. However, the factors that affect C1q binding status are unclear. A total of 519 samples from 129 consecutive kidney transplantation patients during 8 years of dynamic follow-up were collected for HLA antibody (Ab) screening and C1q detection. Among the detected HLA Abs, the majority were class II, and the DQ subtypes composed the highest proportion. The C1q-binding Abs were all HLA-II, and the DQ subtypes had the highest rate of C1q positivity. With a cutoff mean fluorescence intensity (MFI) value of 7349, the sensitivity and specificity of detecting C1q-binding Abs from all HLA-II Abs were 84.48% and 83.56%, respectively. Additionally, C1q is more likely to be bound by DSA than non-donor-specific antibody (NDSA). Compared with free DSA/NDSA, the MFI values of C1q-binding DSA/NDSA are more closely correlated with serum creatinine levels and reflect the effect of anti-antibody-mediated rejection treatment more sensitively. HLA-II Abs (particularly DQ subtypes), high titers of Abs, and DSA are important relevant factors of C1q positivity. The MFI value of C1q-binding DSA may be a useful clinical indicator of HLA antibody-mediated graft injury before the appearance of histologically typical humoral rejection.

Role of Pretransplant Complement-fixing Donor-specific Antibodies Identified by C1q Assay in Kidney Transplantation

BackgroundKidney transplant recipients who have pretransplant donor-specific human leukocyte antigen (HLA) antibodies have greater risk for developing allograft rejection and allograft loss. However, there is a varied effect of graft injury among patients with pretransplantation donor-specific antibodies (DSA). The difference of complement activating ability may be the reason why some DSA are detrimental to kidney allograft. This study aimed to investigate the association between pretransplantation C1q-binding DSA and clinical outcomes. MethodsThis retrospective study included 48 pretransplant sera from kidney transplant recipients who had pretransplant DSA with negative complement-dependent cytotoxic (CDC) crossmatches. The IgG DSA testing and C1q testing were performed on a Luminex platform with single antigen bead assay. The clinical outcomes between C1q-positive and C1q-negative groups were compared. ResultsC1q-positive DSA were detected in 12 out of 48 patients (25%). The incidences of antibody-mediated rejection (AMR) were higher among patients with C1q-positive DSA than patients with C1q-negative DSA (66.7% vs 41.7%). Nevertheless, there were no statistically significant associations between C1q-DSA and AMR (odds ratio 2.8, 95% CI 0.68–11.6, P = .13) and between C1q-DSA and graft loss (odds ratio 0.52, 95% CI 0.09–2.89, P = .44). The C1q-positive DSA group had significantly higher IgG DSA MFI than the C1q-negative DSA group (P < .001). ConclusionC1q-binding ability of DSA in pretransplant sera of kidney recipients was not associated with antibody-mediated rejection and graft loss post-transplantation. In contrast with the clinical relevance of C1q testing in the post-transplantation setting, C1q testing in pretransplant sera has limited use for immunological risk assessment.

LBP34: ANTI-HUMAN GLOBULIN (AHG) ENHANCED C1q ASSAY IMPROVES DETECTION OF DONOR SPECIFIC HLA ANTIBODIES (DSA) IN HEART TRANSPLANT RECIPIENTS WITH ANTIBODY MEDIATED REJECTION

Aim The C1qScreen assay detects complement binding HLA antibodies. Recent studies in cardiac transplant recipients suggest that the presence of C1q positive donor specific antibodies (DSA) is associated with increased risk of antibody mediated rejection (AMR) early post-transplant. However, in some patients with documented AMR, C1q binding DSA are not detected suggesting poor sensitivity of the C1qScreen. In this study we compared the ability to detect DSA by the standard C1qScreen vs the anti-human globulin (AHG) enhanced C1q assay in a cohort of 37 heart transplant recipients with AMR. Methods 37 heart transplant recipients with biopsy proven AMR were studied. Sera were collected at the time of AMR and screened for the presence of DSA using the standard C1qScreen, the AHG enhanced C1q and the LABScreen single antigen bead (SAB)-IgG assay. The number of DSA detected and the average DSA MFI were compared. Results The C1qScreen failed to identify DSA in 14/37 (38%) of patients with biopsy-proven, SAB-IgG positive and/or C4d positive, AMR (Fig. 1). In contrast, the AHG enhanced C1q assay identified DSA in the majority of patients (32/37; 86.5%), approaching the rate of DSA detected by the SAB-IgG assay (34/37; 92%). The average number of DSA/patient identified was also improved with the AHG enhanced C1q assay (2.47 vs 1.56 DSA/patient; AHG enhanced C1q vs C1qScreen). Finally, the mean MFI of DSA was significantly increased (22,191.3 +/− 7454 AHG enhanced C1q vs 11,993.6 +/− 7608 C1qScreen; p 〈 0.001; Fig. 2) confirming that the sensitivity of the AHG enhanced C1q assay is improved. Conclusions The C1qScreen failed to detect DSA in a significant number of heart transplant recipients with biopsy proven AMR and thus, cannot be used to accurately detect pathogenic DSA. The AHG enhanced C1q assay was more sensitive, identifying DSA in the majority of AMR patients and improving detection of low level antibodies. Based on our findings, the AHG enhanced C1q assays may be useful in post-transplant monitoring to detect pathogenic DSA.

De Novo C1q-Binding Donor-Specific Antibody (DSA) in Pediatric Renal Transplant Recipients.

De Novo C1q-Binding Donor-Specific Antibody (DSA) in Pediatric Renal Transplant Recipients.

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To determine the incidence and clinical significance of donor specific antibodies (DSA) in renal allograft recipients with functioning grafts after more than 10 years post-transplantation. HLA antibody screening and identification were performed using One Lambda Single Antigen Bead (SAB) assay. Antibody capacity to fix complement was tested using the C1q assay (One Lambda). Serum samples were obtained from 182 recipients (mean age 43, female 35%, re-transplants 10%, live donor transplants 52%) with functioning grafts after more than 10 years post-transplantation (median time from transplantation 14 yrs, range 10-32 years). All recipients had a negative CDC crossmatch at the time of transplantation. After >10 years post-transplantation, 47% of the patients showed no evidence of sensitization to HLA antigens (cPRA ⩽ 10%, Ab-), 26% displayed cPRA > 10% in the absence of DSA (Ab+DSA-), and 25% displayed cPRA > 10% with DSA (Ab+DSA+). DSA directed to HLA class I, class II or both were identified in 9%, 14% and 2% of patients, respectively. The antibodies most frequently observed were directed to donor DQ antigens (8% of patients). To determine whether DSA had the capacity to bind complement, DSA+ sera were tested using the C1q assay. C1q binding DSA were observed in 47% of the DSA containing sera. Current serum creatinine levels were significantly higher in the Ab+DSA+ group compared to Ab- or Ab+DSA- group. However, there was no difference between creatinine levels in patients with C1q versus non-C1q binding DSA [ Table 1 ]. These results indicate that there is a close correlation between DSA detected late post-transplantation and graft function. Thus, DSA monitoring may assist in the long term management of renal transplant recipients and identifies patients with DSA who should not be considered for reduction in immunosuppression.