C1q-fixing human leukocyte antigen antibodies are specific for predicting transplant glomerulopathy and late graft failure after kidney transplantation. Transplantation. 2011;91:342-347. [PMID: 21116220 DOI: 10.1097/tp.0b013e318203fd26]

C1q-Fixing De Novo Donor Specific Antibodies in Therapeutic Management of Chronic Antibody-Mediated Rejection Postkidney Transplantation

BACKGROUNDS

Evidence for C1q-fixing donor-specific antibodies (DSA) after chronic antibody-mediated rejection (CABMR) treatment is lacking. We investigated if C1q-DSA could predict therapy response in patients with biopsy-proven CABMR.

MATERIAL AND METHODS

Twenty kidney transplant patients with late-onset DSA were enrolled. Patients with biopsy-proven CABMR received three plasma pheresis sessions, one dose of rituximab (375 mg/m2), and steroid pulse therapy. We monitored IgG-DSA, C1q-DSA, and renal graft function for >2 years post-CABMR treatment. Patients with C1q-DSA mean fluorescence intensity (MFI) decreased by less than 50% post-treatment were classified as C1q-nonresponders. We compared Banff classification scores (g, ptc, cg, c4d) before and 6 months after treatment.

RESULTS

Fourteen (70%) of 20 patients were C1q-DSA positive. The MFIs of IgG-DSA and C1q-DSA before treatment were significantly higher in the C1q-DSA positive group than in the negative group, at 20,035 and 10,918 (P = .008) and 17,702 and 21 (P < .001), respectively. Fifteen patients (75%) were diagnosed with CABMR via biopsy, and 12 patients received rejection therapy. Five (41.7%) patients were C1q-responders and seven (58.3%) were C1q-nonresponders. The MFIs of C1q-DSA before treatment were not significantly different between the two groups (11,521 vs. 13,985). Renal graft function was stable after treatment in C1q-responders for 3 years. In contrast, renal graft function tended to deteriorate in C1q-nonresponders. Biopsy showed improvement in scores in 75% of C1q-responders while deterioration in scores in 42.9% of C1q-nonresponders.

CONCLUSIONS

C1q-DSA may be a good predictor of outcomes after CABMR treatment.

Immunopathology of Corneal Allograft Rejection and Donor-Specific Antibodies (DSAs) as Immunological Predictors of Corneal Transplant Failure

Despite tremendous developments in the field of laboratory testing in transplantation, the rules of eligibility for corneal transplantation still do not include typing of human leukocyte antigens (HLAs) in the donor and recipient or detection of donor-specific antibodies (DSAs) in the patient. The standard use of diagnostic algorithms is due to the cornea belonging to immunologically privileged tissues, which usually determines the success of transplantation of this tissue. A medical problem is posed by patients at high risk of transplant rejection, in whom the immune privilege of the eye is abolished and the risk of transplant failure increases. Critical to the success of transplantation in patients at high risk of corneal rejection may be the selection of an HLA-matched donor and recipient, and the detection of existing and/or de novo emerging DSAs in the patient. Incorporating the assessment of these parameters into routine diagnostics may contribute to establishing immune risk stratification for transplant rejection and effective personalized therapy for patients.

ASTCT Consensus Recommendations on Testing and Treatment of Patients with Donor-specific Anti-HLA Antibodies

Donor-specific anti-HLA antibodies (DSA) are an important cause of engraftment failure and may negatively impact survival outcomes of patients receiving allogeneic hematopoietic stem cell transplantation (HSCT) using an HLA-mismatched allograft. The incidence of DSA varies across studies, depending on individual factors, detection or identification methods and thresholds considered clinically relevant. Although DSA testing by multiplex bead arrays remains semiquantitative, it has been widely adopted as a standard test in most transplant centers. Additional testing to determine risk of allograft rejection may include assays with HLA antigens in natural conformation, such as flow cytometric crossmatch, and/or antibody binding assays, such as C1q testing. Patients with low level of DSA (<2,000 mean fluorescence intensity; MFI) may not require treatment, while others with very high level of DSA (>20,000 MFI) may be at very high-risk for engraftment failure despite current therapies. By contrast, in patients with moderate or high level of DSA, desensitization therapy can successfully mitigate DSA levels and improve donor cell engraftment rate, with comparable outcomes to patients without DSA. Treatment is largely empirical and multimodal, involving the removal, neutralization, and blocking of antibodies, as well as inhibition of antibody production to prevent activation of the complement cascade. Desensitization protocols are based on accumulated multicenter experience, while prospective multicenter studies remain lacking. Most patients require a full intensity protocol that includes plasma exchange, while protocols relying only on rituximab and intravenous immunoglobulin may be sufficient for patients with lower DSA levels and negative C1q and/or flow cytometric crossmatch. Monitoring DSA levels before and after HSCT could guide preemptive treatment when high levels persist after stem cell infusion. This paper aims to standardize current evidence-based practice and formulate future directions to improve upon current knowledge and advance treatment for this relatively rare, but potentially serious complication in allogeneic HSCT recipients.

Clinical Outcome of Kidney Transplant Recipients with C1q-Binding De Novo Donor Specific Antibodies: A Single-Center Experience

Complement activation by HLA antibodies is a key component of immune-mediated graft injury. We examined the clinical outcomes of kidney transplant recipients with complement-fixing de novo donor-specific antibodies (dnDSA) who were followed in our center. The C1q-binding ability was retrospectively assessed in 69 patients with dnDSA and mean fluorescence intensity (MFI) values > 2000 out of the 1325 kidney transplant recipients who were screened for DSA between 2015 and 2019. Luminex IgG single antigen beads (SAB)and C1q-SAB assays (One Lambda) were used. C1q-binding dnDSA was identified in 32/69 (46.4%) of the patients. Significantly higher MFI values were observed in C1q-positive DSA (18,978 versus 5840, p < 0.001). Renal graft biopsies were performed in 43 of the kidney transplant recipients (62.3%) with allograft dysfunction. Antibody-mediated rejection (ABMR) was detected in 29/43 (67.4%) of the patients. The incidence of ABMR was similar among patients with C1q-binding and non-C1q-binding DSA (51.7% vs. 48.3%, p = 0.523). Graft loss occurred in 30/69 (43.5%) of the patients at a median time of 82.5 months (IQR 45-135) from DSA detection. C1q-binding DSA was present in more patients who experienced graft loss (53.1% vs. 35.1%, p = 0.152). Higher MFI values and inferior clinical outcomes occurred in most of the kidney transplant recipients with C1q-binding dnDSA.

Association Between De Novo C1q-Binding Donor-Specific Anti-HLA Antibodies and Clinical Outcomes After Kidney Transplantation: A Meta-Analysis

BACKGROUND

Donor-specific antibodies (DSAs) are recognized as an important factor of kidney allograft loss as a subsequent event of antibody-mediated rejection (AMR). The clinical relevance of de novo DSAs (dnDSAs) after kidney transplant, particularly in their ability to bind C1q, has been widely investigated to various extents among studies. A recent study was performed to examine the association between C1q-binding dnDSAs and succeeding clinical events after kidney transplant.

METHODS

A meta-analysis of studies published before April 2021 was conducted from PubMed, Science Direct, and Cochrane databases. Publications on dnDSA after kidney transplant focusing on differentiation between C1q-binding and non-C1q-binding were included. The outcomes analyzed were AMR rate and allograft loss. Studies using preformed DSA were excluded. The pooled risk ratio and 95% confidence interval (CI) were analyzed using Mantzel-Haenzel method, and the I2 value was used to determine the heterogeneity of the studies. Data analysis was conducted using Review Manager 5.3.

RESULTS

A total of 535 patients from 13 studies who developed dnDSA after kidney transplant were analyzed. Among these, 239 (44.7%) had C1q-binding and 296 (55.3%) had non-C1q-binding dnDSA. Acute AMR was found in 59.2% (97/164) of the C1q-binding group and in 28.8% (49/170) of the non-C1q-binding group (risk ratio [RR], 0.58 [95% CI, 0.39-0.85], P = .006, I2 = 58%). Chronic AMR was found in 50% (19/38) of the C1q-binding group and in 16.9% (11/65) of the non-C1q-binding group (RR, 0.39 [95% CI, 0.21-0.71], P = .002, I2 = 0%). Allograft loss was found in 62.2% (74/119) of the C1q-binding group and in 34.1% (60/176) of the non-C1q-binding group (RR, 0.57 [95% CI, 0.38-0.85], P = .006, I2 = 61%).

CONCLUSIONS

This meta-analysis demonstrates that patients who developed C1q-binding dnDSA display an increased risk of AMR and allograft loss compared with those with non-C1q-binding dnDSA. Therefore, C1q-binding dnDSAs are associated with inferior outcomes after kidney transplant.

Immunology and Donor-Specific Antibodies in Corneal Transplantation

The first human corneal transplantation was performed in 1905 by Eduard Zirm in the Olomouc Eye Clinic, now Czech Republic. However, despite great advancements in microsurgical eye procedures, penetrating keratoplasty in high-risk patients (e.g., vascularized or inflamed corneal tissue, consecutive transplants) remains a challenge. The difficulty is mainly due to the risk of irreversible allograft rejection, as an ocular immune privilege in these patients is abolished and graft rejection is the main cause of corneal graft failure. Therefore, tailored immunosuppressive treatment based on immunological monitoring [e.g., donor-specific antibodies (DSA)] is considered one of the best strategies to prevent rejection in transplant recipients. Although there is indirect evidence on the mechanisms underlying antibody-mediated rejection, the impact of DSA on cornea transplantation remains unknown. Determining the role of pre-existing and/or de novo DSA could advance our understanding of corneal graft rejection mechanisms. This may help stratify the immunological risk of rejection, ultimately leading to personalized treatment for this group of transplant recipients.

C1q binding to surface-bound IgG is stabilized by C1r2s2 proteases

Antibody-dependent complement activation plays a major role in various pathophysiological processes in our body, including infection, inflammation, autoimmunity, and transplant rejection. In order to activate complement, antibodies should bind to target cells and recruit complement component C1. C1 is a large, multimolecular complex that consists of the antibody recognition protein C1q and a heterotetramer of proteases (C1r₂s₂). Although it is believed that interactions between C1 and IgGs are solely mediated by C1q, we here show that C1r₂s₂ proteases affect the capacity of C1q to form an avid complex with surface-bound IgG molecules. Furthermore, we demonstrate that C1q–IgG stability is influenced by IgG oligomerization and that promoting IgG oligomerization improves phagocytosis of the pathogenic bacterium Staphylococcus aureus.

Complement is an important effector mechanism for antibody-mediated clearance of infections and tumor cells. Upon binding to target cells, the antibody’s constant (Fc) domain recruits complement component C1 to initiate a proteolytic cascade that generates lytic pores and stimulates phagocytosis. The C1 complex (C1qr₂s₂) consists of the large recognition protein C1q and a heterotetramer of proteases C1r and C1s (C1r₂s₂). While interactions between C1 and IgG-Fc are believed to be mediated by the globular heads of C1q, we here find that C1r₂s₂ proteases affect the capacity of C1q to form an avid complex with surface-bound IgG molecules (on various 2,4-dinitrophenol [DNP]-coated surfaces and pathogenic Staphylococcus aureus). The extent to which C1r₂s₂ contributes to C1q–IgG stability strongly differs between human IgG subclasses. Using antibody engineering of monoclonal IgG, we reveal that hexamer-enhancing mutations improve C1q–IgG stability, both in the absence and presence of C1r₂s₂. In addition, hexamer-enhanced IgGs targeting S. aureus mediate improved complement-dependent phagocytosis by human neutrophils. Altogether, these molecular insights into complement binding to surface-bound IgGs could be important for optimal design of antibody therapies.

Impact of C1q fixing donor-specific antibodies on renal transplant outcome

Not all anti-HLA donor-specific antibodies (HLA-DSAs) are detrimental to renal allograft. In this context, the C1q complement activating ability of antibodies appears to be an important parameter to distinguish clinically inert versus detrimental DSAs. We evaluated sera of 206 consecutive primary live donor renal transplant recipients before transplant and at post-operative day 7, 30, 90, 180 and at the time of graft dysfunction for quantifying HLA-DSAs using single antigen bead assay on a Luminex platform. Patients positive for these antibodies with an MFI >500 were further screened for C1q fixing nature of DSA. Fourteen of the 18 antibody-positive patients had C1q fixing DSA with MFI value >5000. Only 4 antibody-positive patients did not have C1q fixing DSA. The MFI values of DSA detected by C1q assay were generally higher at least by 25% than those detected by the conventional IgG-SAB assay. Twelve of the 14 patients (85.71%) with C1q+ DSA developed antibody-mediated rejection during the mean follow-up period of 21.43 ± 8.03 months as compared to none of the four C1q-negative DSA (85.71% vs 0%; P = .001). These results suggest deleterious effect of C1q+ DSA vis-à-vis C1q-negative DSA on renal allograft.

Therapies for Chronic Allograft Rejection

Remarkable advances have been made in the pathophysiology, diagnosis, and treatment of antibody-mediated rejection (ABMR) over the past decades, leading to improved graft outcomes. However, long-term failure is still high and effective treatment for chronic ABMR, an important cause of graft failure, has not yet been identified. Chronic ABMR has a relatively different phenotype from active ABMR and is a slowly progressive disease in which graft injury is mainly caused by de novo donor specific antibodies (DSA). Since most trials of current immunosuppressive therapies for rejection have focused on active ABMR, treatment strategies based on those data might be less effective in chronic ABMR. A better understanding of chronic ABMR may serve as a bridge in establishing treatment strategies to improve graft outcomes. In this in-depth review, we focus on the pathophysiology and characteristics of chronic ABMR along with the newly revised Banff criteria in 2017. In addition, in terms of chronic ABMR, we identify the reasons for the resistance of current immunosuppressive therapies and look at ongoing research that could play a role in setting better treatment strategies in the future. Finally, we review non-invasive biomarkers as tools to monitor for rejection.

C3d-Positive Preformed DSAs Tend to Persist and Result in a Higher Risk of AMR after Kidney Transplants

C3d-binding assays have been introduced as methods for the prediction of the presence of complement-binding functional antibodies; however, the prognostic value of C3d-positive preformed donor-specific antibodies (pDSAs) has not been fully evaluated. In this study, we performed a retrospective investigation of the association of pDSAs and their C3d-binding capacity with one-year clinical outcomes. pDSAs were defined as donor-specific antibodies (DSAs) that were produced before kidney transplants (KTs) (pre-pDSAs) or within the first four weeks after KTs, owing to rebound immune response (post-pDSAs). Of 455 adult KT recipients, pre-pDSAs and post-pDSAs were found in 56 (12.3%) and 56 (12.3%) recipients, respectively, and C3d-positive post-pDSAs were found in 13 recipients (2.9%) in total. Approximately half of the C3d-negative pre-pDSAs (37/73, 50.7%) disappeared after transplantation; however, all C3d-positive pre-pDSAs (8/8, 100%) persisted after transplantation despite desensitization (p = 0.008). C3d-positive pDSAs were significantly associated with a higher incidence and risk of AMR (p < 0.001, OR 94.467–188.934). Identification of the C3d-binding activity of pDSAs before and early after KT is important for predicting the persistence of pDSAs and the risk of AMR induced by the presence of pDSAs.

Complement as an Immune Barrier in Platelet Transfusion Refractoriness

Patients with hematological cancers often have low platelet counts because of progressing bone marrow failure or cytostatic therapy. A large fraction of those patients need platelet transfusions, which can be life-saving if bleedings occur and also allow diagnostic and therapeutic interventions. The outcomes of platelet transfusions are not always easy to predict in terms of bleeding control or increase in platelet count. Reasons could be disease-specific factors, fever, or infections leading to platelet consumption, but the immune system may also be involved, in particular, in patients previously immunized against foreign human leukocyte antigens (HLA). Mechanisms underlying immune-mediated platelet destruction in the presence of antibodies again HLA are not well understood in clinical situations. This review discusses the role of complement in platelet refractoriness, with a focus on HLA antibody-mediated platelet refractoriness. We summarize recent work in this area, discuss complement-platelet interactions in general terms, and a suggest a possible role of complement in platelet transfusion in general.

Human Leucocyte Antigen Sensitisation and Its Impact on Transfusion Practice

Human leucocyte antigen (HLA) sensitisation, including the formation of antibodies against HLA, can cause serious effects in patients receiving blood. Under certain circumstances, donor HLA antibodies in the blood product can trigger the patient's granulocytes to release mediators that cause transfusion-associated lung injury (TRALI), a serious complication of transfusion. The HLA systems of both donor and patient are involved in transfusion-associated graft-versus-host disease, which is a rare disease with a high mortality. Patient HLA antibodies can destroy incompatible platelets and may cause refractoriness to platelet transfusion. Identification of a patient's HLA antibody specificities is necessary for issuing compatible platelets to overcome refractoriness. Many techniques for the detection and identification of HLA antibodies have been developed, including complement-dependent cytotoxicity assay, bead-based assays, the platelet adhesion immunofluorescence test, and the monoclonal antibody-specific immobilisation of platelet antigens assay. Different strategies for the selection of HLA-compatible platelets are applied. These strategies depend on the breadth of antibody reactivity and range from avoiding single HLA antigens in the platelet concentrates issued to apheresis of platelets from HLA-identical donors. The mechanisms of HLA sensitisation and the efforts made to provide compatible blood products to sensitised patients are reviewed in this article from the perspective of clinical transfusion medicine.

Circulating B Cells With Memory and Antibody-Secreting Phenotypes Are Detectable in Pediatric Kidney Transplant Recipients Before the Development of Antibody-Mediated Rejection

Development of anti-human leukocyte antigen donor-specific antibodies (DSAs) is associated with antibody-mediated rejection (AMR) and reduced allograft survival in kidney transplant recipients. Whether changes in circulating lymphocytes anticipate DSA or AMR development is unclear.

METHODS

We used time-of-flight mass cytometry to analyze prospectively collected peripheral blood mononuclear cells (PBMC) from pediatric kidney transplant recipients who developed DSA (DSA-positive recipients [DSAPOS], n = 10). PBMC were obtained at 2 months posttransplant, 3 months before DSA development, and at DSA detection. PBMC collected at the same time points posttransplant from recipients who did not develop DSA (DSA-negative recipients [DSANEG], n = 11) were used as controls.

RESULTS

DSAPOS and DSANEG recipients had similar baseline characteristics and comparable frequencies of total B and T cells. Within DSAPOS recipients, there was no difference in DSA levels (mean fluorescence intensity [MFI]: 13 687 ± 4159 vs 11 375 ± 1894 in DSAPOSAMR-positive recipients (AMRPOS) vs DSAPOSAMR-negative recipients (AMRNEG), respectively; P = 0.630), C1q binding (5 DSAPOSAMRPOS [100%] vs 4 DSAPOSAMRNEG [80%]; P = 1.000), or C3d binding (3 DSAPOSAMRPOS [60%] vs 1 DSAPOSAMRNEG [20%]; P = 0.520) between patients who developed AMR and those who did not. However, DSAPOS patients who developed AMR (n = 5; 18.0 ± 3.6 mo post-DSA detection) had increased B cells with antibody-secreting (IgD-CD27+CD38+; P = 0.002) and memory (IgD-CD27+CD38-; P = 0.003) phenotypes compared with DSANEG and DSAPOSAMRNEG recipients at DSA detection.

CONCLUSIONS

Despite the small sample size, our comprehensive phenotypic analyses show that circulating B cells with memory and antibody-secreting phenotypes are present at DSA onset, >1 year before biopsy-proven AMR in pediatric kidney transplant recipients.

Prognostic value of C3d-fixing, preformed donor-specific antibodies in crossmatch-positive living kidney transplantation

The occurrence of acute antibody-mediated rejection (ABMR) is higher in flow cytometric crossmatch (FCXM)-positive patients despite desensitization. Accumulating evidence suggests a correlation between the complement-binding ability of donor-specific antibodies (DSAs) and the risk of ABMR. Here, we investigated the correlation between complement C3d-fixing ability of preformed DSA and ABMR risk, the efficacy of a desensitization protocol for patients with C3d-fixing DSA, and the risk of ABMR in 21 DSA- and FCXM-positive patients. We retrospectively analyzed the C3d-fixing ability and mean fluorescence intensity (MFI) of preformed DSA before and after desensitization. Six patients had non-C3d-fixing DSA and 15 had C3d-fixing DSA. The presence of C3d-fixing DSA before desensitization was correlated with the incidence of acute ABMR within 1 year after transplantation (p = .04) and chronic ABMR (p = .03). Moreover, the MFI of preformed DSA differed between responder and non-responder C3d-fixing DSA after desensitization (p < .0001). The C3d-fixing ability of preformed DSA with low MFI disappeared after desensitization. These results indicate that measuring DSA C3d-fixing ability may identify patients with a high risk of ABMR, especially before desensitization. CLINICAL TRIAL NOTATION: UMIN Clinical Trials Registry (UMIN-CTR) number: UMIN000033449.

B-Cell Activating Factor Predicts Acute Rejection Risk in Kidney Transplant Recipients: A 6-Month Follow-Up Study

B cell activating factor (BAFF) belonging to TNF family is a cytokine that enhances B-cell proliferation and differentiation. Recently, It has been suggested that BAFF might be a potential therapeutic target for treating autoimmune disease. However, the relationship between BAFF and allograft rejection is controversial, and the clinical significance of BAFF in predicting allograft rejection need to be further explored. We conducted 6-month follow-up study to confirm the hypothesis that BAFF might be a risk factor for predicting acute rejection in kidney transplant recipients. At the end of the study, a total of 155 kidney transplant recipients were recruited from October 2015 to October 2017, and classified into acute rejection group (n = 34) and stable renal function group (n = 121) according to their clinical course. We demonstrate that the serum BAFF levels when acute rejection occurred was significantly higher than that in the stable renal function group (2426.19 ± 892.19 vs. 988.17 ± 485.63 pg/mL, P < 0.05). BAFF expression was significantly enhanced in the membrane and cytoplasm of renal tubule epithelial cells in the transplant kidney tissue with acute rejection, and a positive correlation between BAFF and C4d expression was also observed (r = 0.880, P = 0.001). ROC analyses highlight the superiority of serum BAFF level before transplant over those on other post-transplant days in prediction of acute rejection episodes. The sensitivity, specificity and AUC (area under curve) were 83.3, 89.5, and 0.886%, respectively. Kaplan-Meier survival analysis showed that recipients with higher pretransplant BAFF levels had higher acute rejection incidence (P = 0.003). In conclusion, we have identified that BAFF levels are associated with the acute rejection and could be a promising biomarker to predict kidney transplant rejection risks.

Understanding the Correlation Between DSA, Complement Activation, and Antibody-Mediated Rejection in Heart Transplant Recipients

BACKGROUND

Donor-specific HLA antibodies (DSA) are associated with increased rates of rejection and of graft failure in cardiac transplantation. The goal of this study was to determine the association of preformed and posttransplant development of newly detected DSA (ndDSA) with antibody-mediated rejection (AMR) and characterize the clinical relevance of complement-activating DSA in heart allograft recipients.

METHODS

The study included 128 adult and 48 pediatric heart transplant patients transplanted between 2010 and 2013. Routine posttransplant HLA antibody testing was performed by IgG single-antigen bead test. The C3d single-antigen bead assay was used to identify complement-activating antibodies. Rejection was diagnosed using International Society for Heart and Lung Transplantation criteria.

RESULTS

In this study, 22 patients were transplanted with preexisting DSA, and 43 patients developed ndDSA posttransplant. Pretransplant (P < 0.05) and posttransplant (P < 0.001) ndDSA were associated with higher incidence of AMR. Patients with C3d + DSA had significantly higher incidence of AMR compared with patients with no DSA (P < 0.001) or patients with C3d-DSA (P = 0.02). Nine (36%) of 25 patients with AMR developed transplant coronary artery disease compared with 17 (15.9%) of 107 patients without AMR (P < 0.05). Among the 47 patients who received ventricular assistant device (VAD), 7 of 9 VAD+ patients with preformed DSA experienced AMR compared with 7 of 38 VAD+ patients without preformed DSA, indicating presensitization to donor HLA significantly increased the risk of AMR (P < 0.01).

CONCLUSIONS

Preformed and posttransplant ndDSA were associated with AMR. C3d + DSA correlates with complement deposition on the graft and higher risk of AMR which may permit the application of personalized immunotherapy targeting the complement pathway.

Biomarkers in Solid Organ Transplantation

After more than 6 decades of clinical practice, the transplant community continues to research noninvasive biomarkers of solid organ injury to help improve patient care. In this review, we discuss the clinical usefulness of selective biomarkers and how they are processed at the laboratory. In addition, we organize these biomarkers based on specific aims and introduce innovative markers currently under investigation.

Clinical utility of complement-dependent C3d assay in kidney recipients presenting with late allograft dysfunction

The objective of this study was to evaluate the utility of a complement-dependent C3d assay to risk stratify donor-specific antibodies (DSA) in a multicenter cohort of kidney recipients presenting with new-onset clinical dysfunction. A total of 106 subjects with evidence of DSA at a mean period of 5.3 ± 5.0 years posttransplant underwent testing using C3d reagents. C3d positivity was strongly associated with both the peak and sum IgG DSA MFI, with 98.3% (n = 57/58) of strongly reactive sera (peak MFI > 10 000) eliciting a positive signal. Patients with C3d+ DSA had a higher creatinine (P = .03), more significant graft fibrosis (P = .035), and a faster rate of graft loss posttest compared to those with C3d- DSA (P = .05). Subanalysis of patients with low-moderate level DSA confirmed the inferior outcome associated with C3d positivity. Despite the prognostic value of C3d as a stand-alone test, the assay did not provide independent risk prediction after incorporation of graft fibrosis in a multivariate model (P = .94). Overall, C3d offered limited discriminatory value for strong DSA with peak IgG MFI > 10 000 and in patients where histologic data is available, but its utilization may be considered in those with low-moderate level DSA and where an allograft biopsy is not accessible.

Clinical impact of complement (C1q, C3d) binding De Novo donor-specific HLA antibody in kidney transplant recipients

Introduction

Complement binding activity of donor-specific HLA antibodies (DSA) has been suggested as a new tool to stratify immunologic risk in kidney transplantation (KT). The objective of this study was to evaluate the clinical implication of C1q/C3d binding activity of de novo DSA (dnDSA) in KT recipients.

Material and methods

A total of 161 pretransplant DSA-negative recipients were monitored for dnDSA at the time of biopsy. C1q/C3d binding activities of dnDSA were assessed using C1qScreen assay (One lambda, USA) and Lifecodes C3d detection assay (Immucor, USA), respectively. Clinical outcomes including biopsy-proven antibody mediated rejection (AMR), C4d detection and post-biopsy graft survival were investigated.

Results

De-novo DSAs were detected in fifty-four (33.5%) patients (HLA class I only, n = 19; class II only, n = 29; both class I and II, n = 6). Of them, complement binding activities were detected in 26 (48.1%) patients, including 17 C1q+ and 24 C3d+ patients. Both C1q and C3d positivity were associated with increased mean fluorescence intensity values of dnDSA. Complement binding activity of dnDSA enhanced the incidence of AMR (25.0% in C1q-C3d-, 36.4% in C1q+/C3d- or C1q-/C3d+, and 60.0% in C1q+/C3d+ patients) (P <0.001). The incidence of AMR was not different between patients with C1q+ and those with C3d+ dnDSA (64.7%, 11/17 versus 45.8%, 11/24, P = 0.238). In comparison between C1q and C3d assay according to HLA specificity, C1q+ HLA class I ± II dnDSA was the best predictor for AMR (odds ratio: 27.2). C1q+/C3d+ dnDSA was associated with more C4d deposition in allograft tissue and inferior post-biopsy graft survival. Clinical outcomes were not significantly different between C1q+ and C3d+ dnDSA-positive patients.

Conclusion

Detection of complement binding activity using both C1q and C3d assays can be a further prognostic marker for predicting AMR and allograft outcome in dnDSA+ kidney transplant patients.

Functional Fc gamma receptor gene polymorphisms and donor-specific antibody-triggered microcirculation inflammation

Fc-dependent effector mechanisms may contribute to antibody-mediated rejection (ABMR), and distinct gene polymorphisms modifying the function of Fc gamma receptors (FcγRs) may influence the capability of donor-specific antibodies (DSAs) to trigger inflammation. To evaluate the relevance of functional FcγR variants in late ABMR, 85 DSA-positive kidney allograft recipients, who were recruited upon antibody screening of 741 prevalent patients, were genotyped for polymorphisms in FcγRIIA (FCGR2A-H/R₁₃₁ ; rs1801274), FcγRIIIA (FCGR3A-V/F₁₅₈ ; rs396991), and FcγRIIIB (FCGR3B-neutrophil antigen 1 ([NA1]/NA2; rs35139848). Individuals with high-affinity FCGR3A-V₁₅₈ alleles (V/V₁₅₈ or V/F₁₅₈ ) showed a higher rate (and extent) of peritubular capillaritis (ptc) in protocol biopsies than homozygous carriers of the lower-affinity allele (ptc score ≥1: 53.6% vs 25.9%; P = .018). Associations were independent of C1q-binding to DSA or capillary C4d. In parallel, there was a trend toward increased macrophage- and injury-repair response-associated transcript subsets. Kidney function over 24 months, however, was not different. In support of a functional role of FcγRIIIA polymorphism, NK92 cells expressing FCGR3A-V₁₅₈ produced >2 times as much interferon gamma upon incubation with HLA antibody-coated cells as those expressing FCGR3A-F₁₅₈ . FcγRIIA and FcγRIIIB polymorphisms were not associated with allograft morphology. Our data suggest that the presence of high-affinity FcγRIIIA variants may favor DSA-triggered microcirculation inflammation.

IGG3 anti-HLA donor-specific antibodies and graft function in pediatric kidney transplant recipients

Anti-HLA DSAs are associated with ABMR and graft loss in KT recipients, yet the influence of DSA IgG subclass on outcomes in pediatric KT recipients is not completely understood. We performed a single-center retrospective chart review of pediatric KT recipients with anti-HLA DSAs, aiming to study the association between specific DSA IgG subclasses and graft outcomes, including ABMR and significant graft dysfunction (graft loss or 50% decrease in eGFR). Thirty-six patients (mean age 15.4y) with DSAs initially detected 1 month-14.3 years post-transplantation were followed for a median of 2.8 years. Rates of IgG1, 2, 3, and 4 subclass detection were 92%, 33%, 58%, and 25%, respectively. Twenty-two patients (61%) had clinical ABMR, whereas 19% had subclinical ABMR, and 13 (36%) experienced significant graft dysfunction. Patients with IgG3+ DSAs had a higher risk of graft dysfunction compared with IgG3- patients (52% vs 13%, P = .03). In a multiple Cox proportional regression analysis, the presence of IgG3+ DSA was independently associated with significant graft dysfunction (HR 10.45, 95% CI 1.97-55.55, P = .006). In conclusion, IgG3 subclass DSAs are associated with graft dysfunction and may be useful for risk stratification and treatment decisions in DSA-positive pediatric KT recipients.

C3d-binding Donor-specific HLA Antibody Is Associated With a High Risk of Antibody-mediated Rejection and Graft Loss in Stable Kidney Transplant Recipients: A Single-center Cohort Study

BACKGROUND

One risk factor for antibody-mediated rejection (ABMR) and poor outcome after kidney transplantation is donor-specific anti‒human leukocyte antigen (anti-HLA) antibodies (DSAs). In this study we sought to determine whether the presence of DSAs that bind complement component C3d could better predict ABMR and graft loss in stable kidney transplant recipients (KTRs).

METHODS

We included 220 stable KTRs in this study and screened them for DSAs from July 2013 to July 2016.

RESULTS

Of the 220 KTRs, DSAs were detected in 24 (10.9%). The incidence of ABMR was 3.6% (8 of 220) overall, and C3d-DSA‒positive KTRs had a significantly higher incidence than SA-DSA‒positive KTRs (63.3% vs 38.9%, P = .03). Most C3d-binding DSAs were anti-HLA class II antibodies (11 of 13, 84.6%). Class II C3d-binding DSA was also significantly associated with graft failure on multivariate analysis, as were ABMR, chronic ABMR, and high serum creatinine. Class II C3d-binding DSA was also significantly associated with lower graft survival after ABMR.

CONCLUSION

C3d-binding DSA, especially class II, was significantly associated with the risk of ABMR and graft loss in stable KTRs. We suggest that monitoring of stable KTRs for C3d-binding DSA, followed by biopsy, could aid in early recognition of ABMR and prevention of graft loss.

Correlations between donor-specific antibodies and non-adherence with chronic active antibody-mediated rejection phenotypes and their impact on kidney graft survival

Chronic-active antibody-mediated rejection (CAABMR) is associated with poor kidney graft survival and has no clear effective treatment. Forty-one cases of CAABMR were detected in indication graft biopsies and evaluated according to current Banff classification. We investigated the impact of concurrent donor-specific antibodies (DSA) and their characteristics, together with non-adherence regarding immunosuppression on CAABMR histopathological phenotypes and prognosis. Twenty-four (59%) patients had detectable DSA at biopsy, with 15 of them being considered non-adherent. Graft function at biopsy was similar in DSA (+) and (-) patients. DSA (+) patients had significantly higher tubulointerstitial inflammation (i and ti) and acute humoral (g+ptc+v+C4d) composite score than DSA (-). DSA (+)/non-adherent cases presented additionally with increased microvascular inflammation (ptc and v), besides having a distinctively lower ah score. C1q DSA strength was higher (P = .046) in non-adherent patients and correlated closely with C4d score (P = .002). Lower graft function and ah score, higher proteinuria and ci + ct score, and, separately per each model, DSA (+) (HR = 2.446, P = .034), DSA (+)/non-adherent (HR = 3.657, P = .005) and DSA (+)/C1q (+) (HR = 4.831, P = .003) status were independent predictors of graft failure. CAABMR with concomitant DSA pose a higher risk of graft failure. Adherence should be evaluated, and histopathological phenotyping and DSA characterization may add critical information.

The management of antibodies in heart transplantation: An ISHLT consensus document

Despite the successes from refined peri-operative management techniques and immunosuppressive therapies, antibodies remain a serious cause of morbidity and mortality for patients both before and after heart transplantation. Patients awaiting transplant who possess antibodies against human leukocyte antigen are disadvantaged by having to wait longer to receive an organ from a suitably matched donor. The number of pre-sensitized patients has been increasing, a trend that is likely due to the increased use of mechanical circulatory support devices. Even patients who are not pre-sensitized can go on to produce donor-specific antibodies after transplant, which are associated with worse outcomes. The difficulty in managing antibodies is uncertainty over which antibodies are of clinical relevance, which patients to treat, and which treatments are most effective and safe. There is a distinct lack of data from prospective trials. An international consensus conference was organized and attended by 103 participants from 75 centers to debate contentious issues, determine the best practices, and formulate ideas for future research on antibodies. Prominent experts presented state-of-the-art talks on antibodies, which were followed by group discussions, and then, finally, a reconvened session to establish consensus where possible. Herein we address the discussion, consensus points, and research ideas.

Application, technical issues, and interpretation of C1q for graft outcome

Significant interest and controversy surround the use of C1q for determining risk of antibody-mediated rejection (AMR) and graft loss. Alternate models for predicting outcomes have been proposed. This review focuses on the correlation of currently utilized assays for outcome, together with the technical and theoretical limitations, to distill current thinking.

The European Society for Blood and Marrow Transplantation (EBMT) Consensus Guidelines for the Detection and Treatment of Donor-specific Anti-HLA Antibodies (DSA) in Haploidentical Hematopoietic Cell Transplantation

Haploidentical donors are now increasingly considered for transplantation in the absence of HLA-matched donors or when an urgent transplant is needed. Donor-specific anti-HLA antibodies (DSA) have been recently recognized as an important barrier against successful engraftment of donor cells, which can affect transplant survival. DSA appear more prevalent in this type of transplant due to higher likelihood of alloimmunization of multiparous females against offspring's HLA antigens, and the degree of mismatch. Here we summarize the evidence for the role of DSA in the development of primary graft failure in haploidentical transplantation and provide consensus recommendations from the European Society for Blood and Marrow Transplant Group on testing, monitoring, and treatment of patients with DSA receiving haploidentical hematopoietic progenitor cell transplantation.

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.

Antibody-mediated rejection: New approaches in prevention and management

Despite the success of desensitization protocols, antibody-mediated rejection (AMR) remains a significant contributor to renal allograft failure in patients with donor-specific antibodies. Plasmapheresis and high-dose intravenous immunoglobulin have proved to be effective treatments to prevent and treat AMR, but irreversible injury in the form of transplant glomerulopathy can commonly manifest months to years later. There is an unmet need to improve the outcomes for patients at risk for AMR. Updated Banff criteria now take into account the increasing understanding of the complex and heterogeneous nature of AMR phenotypes, including the timing of rejection, subclinical and chronic AMR, C4d-negative AMR, and antibody-mediated vascular rejection. Treatment for AMR is not standardized, and there is little in the way of evidence-based treatment guidelines. Refining more precisely the mechanisms of injury responsible for different AMR phenotypes and establishing relevant surrogate endpoints to facilitate more informative studies will likely allow for more accurate determination of prognosis and efficacious intervention using new therapeutic approaches. In addition to plasma exchange and intravenous immunoglobulin, a number of other add-on therapies have been tried in small studies without consistent benefit, including anti-CD20, proteasome inhibitors, complement inhibitors, anti-interleukin-6 receptor blockers, and immunoglobulin G-degrading enzyme of Streptococcus pyogenes (called IdeS).

Evidence for an important role of both complement-binding and noncomplement-binding donor-specific antibodies in renal transplantation

PURPOSE OF REVIEW

The review describes the current clinical relevance of circulating anti-human leukocyte antigen (anti-HLA) antibodies in kidney transplantation and discusses recent improvements in their characterization that provide new insights into the identification and management of important clinical outcomes.

RECENT FINDINGS

Recent studies addressing the relationships between donor-specific anti-HLA antibody (HLA-DSA) properties (i.e., their strength, complement-binding capacity, and IgG subclass composition) and allograft injury and survival have highlighted their relevance in the prediction of antibody-mediated injury and allograft loss.

SUMMARY

Antibody-mediated rejection is the leading cause of kidney allograft loss. Although considerable experimental and clinical evidence suggests a causal effect of circulating HLA-DSAs in antibody-mediated rejection and allograft failure, HLA-DSAs induce a wide spectrum of injuries to the allograft that illustrate the need to delineate the characteristics of HLA-DSAs that confer pathogenesis. Current risk stratification is based on HLA-DSA characteristics, including antibody specificity, HLA class, and strength. Recently, the complement-binding capacity of HLA-DSAs has been recognized as a clinically relevant marker for predicting pathogenicity and allograft loss. Emerging data also support a role for HLA-DSA IgG subclass composition in discriminating distinct patterns of antibody-mediated injury. This progress in our understanding of HLA-DSA pathogenicity provides new tools to stratify individual immunological risks. However, specific prospective studies addressing immunological risk stratification in large and unselected populations are required to define the clinical benefit and cost-effectiveness of such a comprehensive assessment of HLA-DSAs before implementation in current clinical practice.

Real Time Central Assessment of Kidney Transplant Indication Biopsies by Microarrays: The INTERCOMEX Study

The authors conducted a prospective trial to assess the feasibility of real time central molecular assessment of kidney transplant biopsy samples from 10 North American or European centers. Biopsy samples taken 1 day to 34 years posttransplantation were stabilized in RNAlater, sent via courier overnight at ambient temperature to the central laboratory, and processed (29 h workflow) using microarrays to assess T cell- and antibody-mediated rejection (TCMR and ABMR, respectively). Of 538 biopsy samples submitted, 519 (96%) were sufficient for microarray analysis (average length, 3 mm). Automated reports were generated without knowledge of histology and HLA antibody, with diagnoses assigned based on Molecular Microscope Diagnostic System (MMDx) classifier algorithms and signed out by one observer. Agreement between MMDx and histology (balanced accuracy) was 77% for TCMR, 77% for ABMR, and 76% for no rejection. A classification tree derived to provide automated sign-outs predicted the observer sign-outs with >90% accuracy. In 451 biopsy samples where feedback was obtained, clinicians indicated that MMDx more frequently agreed with clinical judgment (87%) than did histology (80%) (p = 0.0042). In 81% of feedback forms, clinicians reported that MMDx increased confidence in management compared with conventional assessment alone. The authors conclude that real time central molecular assessment is feasible and offers a useful new dimension in biopsy interpretation. ClinicalTrials.gov NCT#01299168.

Complement-Activating Anti-HLA Antibodies in Kidney Transplantation: Allograft Gene Expression Profiling and Response to Treatment

Complement-activating anti-HLA donor-specific antibodies (DSAs) are associated with impaired kidney transplant outcome; however, whether these antibodies induce a specific rejection phenotype and influence response to therapy remains undetermined. We prospectively screened 931 kidney recipients for complement-activating DSAs and used histopathology, immunostaining, and allograft gene expression to assess rejection phenotypes. Effector cells were evaluated using in vitro human cell cultures. Additionally, we assessed the effect of complement inhibition on kidney allograft rejection phenotype and the clinical response to complement inhibition in 116 independent kidney recipients with DSAs at transplant receiving rejection prophylaxis with eculizumab or standard of care (plasma exchange and intravenous Ig) at ten international centers. The histomolecular rejection phenotype associated with complement-activating DSA was characterized by complement deposition and accumulation of natural killer cells and monocytes/macrophages in capillaries and increased expression of five biologically relevant genes (CXCL11, CCL4, MS4A7, MS4A6A, and FCGR3A) indicative of endothelial activation, IFNγ response, CD16-mediated natural killer cell activation, and monocyte/macrophage activation. Compared with standard of care, eculizumab specifically abrogated this histomolecular rejection phenotype and associated with a decreased 3-month rejection incidence rate in patients with complement-activating DSAs (56%; 95% confidence interval [95% CI], 38% to 74% versus 19%; 95% CI, 8% to 35%; P=0.001) but not in those with noncomplement-activating DSAs (9%; 95% CI, 2% to 25% versus 13%; 95% CI, 2% to 40%; P=0.65). In conclusion, circulating complement-activating anti-HLA DSAs are associated with a specific histomolecular kidney allograft rejection phenotype that can be abrogated by complement inhibition.

Kidney Transplant With Low Levels of DSA or Low Positive B-Flow Crossmatch: An Underappreciated Option for Highly Sensitized Transplant Candidates

BACKGROUND

Avoiding donor-specific antibody (DSA) is difficult for sensitized patients. Improved understanding of the risk of low level DSA is needed.

METHODS

We retrospectively compared the outcomes of 954 patients transplanted with varied levels of baseline DSA detected by single antigen beads and B flow cytometric crossmatch (XM). Patients were grouped as follows: -DSA/-XM, +DSA/-XM, +DSA/low +XM, +DSA/high +XM, and -DSA/+XM and followed up for a mean of 4.1 ± 1.9 years (similar among groups, P = 0.49).

RESULTS

Death-censored allograft survival was similar in all groups except the +DSA/high +XM group, which was lower at 79.1% versus 96.2% in the -DSA/-XM group (P < 0.01). The incidence of chronic antibody-mediated rejection (CAMR) based on surveillance biopsy was higher with increasing DSA (8.2% -DSA/-XM, 17.0% +DSA/-XM, 30.6% +DSA/low +XM, and 51.2% +DSA/high +XM, P < 0.01), but similar in groups without baseline DSA (8.1% -DSA/-XM vs 15.4% -DSA/+XM, P = 0.19). Having a calculated panel-reactive antibody (cPRA) of 80% or greater was independently associated with CAMR (hazard ratio, 5.2; P = 0.03) even when DSA was undetected at baseline. By 2 years posttransplant, the incidence of CAMR was 19.4% in patients with cPRA of 80% or greater and undetected DSA and negative XM at baseline.

CONCLUSIONS

Kidney transplantation with low-level DSA with or without a low positive XM is a reasonable option for highly sensitized patients and may be advantageous compared with waiting for a negative XM deceased donor. The risk for CAMR is low in patients with no DSA even if the XM is positive. Patients with cPRA of 80% or greater are at risk for CAMR even if no DSA is detected.

Plasma C4d+ Endothelial Microvesicles Increase in Acute Antibody-Mediated Rejection

BACKGROUND

Antibody-mediated rejection (AMR) is a major cause of kidney allograft loss. Currently, AMR diagnosis relies on biopsy which is an invasive procedure. A noninvasive biomarker of acute AMR could lead to early diagnosis and treatment of this condition and improve allograft outcome. Microvesicles are membrane-bound vesicles released from the cell surface after injury. We hypothesized that because AMR is associated with allograft endothelial injury and C4d deposition, plasma microvesicles positive for endothelial (CD144) marker and C4d are increased in this condition.

METHODS

We studied microvesicle concentration in the plasma of 95 kidney transplant patients with allograft dysfunction and compared with 23 healthy volunteers. Biopsy diagnosis and scoring was performed using Banff classification.

RESULTS

In the 28 subjects with AMR, the density of C4d+/CD144+ microvesicles was on average 11-fold (P = 0.002) higher than transplant recipients with no AMR and 24-fold (P = 0.008) than healthy volunteers. Densities of C4d+ and C4d+/annexin V+ (C4d+/AVB+) microvesicles were also increased in AMR patients compared with no AMR and healthy subjects. C4d+/AVB+ microvesicles correlated with AMR biopsy severity. Nine patients with acute AMR that received treatment showed a mean 72% decrease (P = 0.01) in C4d+/CD144+ microvesicle concentration compared with pretreatment values.

CONCLUSIONS

Quantification of plasma C4d+ microvesicles provides information about presence of AMR, its severity and response to treatment in transplant patients.

Detection of T and B cells specific complement-fixing alloantibodies using flow cytometry: A diagnostic approach for a resource limited laboratory

BACKGROUND AND OBJECTIVES

Various methods have been reported for the detection of antibodies in recipient sera, which can be human leukocyte antigens (HLAs) or non-HLA specific, complement- or noncomplement fixing, as well as donor T (HLA-Class-I) and/or B cell (HLA-Class-I and II) specific. These alloantibodies play a pivotal role in antibody-mediated renal transplantation rejection. Deposition of C4d in peritubular capillaries of a kidney biopsy is a marker of antibody-mediated rejection. The C4d flow-panel reactive antibodies (PRAs) are a screening method for HLA-specific and complement fixing antibodies. However, the method is limited by the lack of donor specificity.

DESIGN AND SETTINGS

Here, we present a new and simple flow cytometric method referred to as C4d-flow cytometry crossmatch (C4d-FCXM) for the detection of donor-specific (T and/or B cell) and C4d-fixing alloantibodies.

RESULTS

The method was applied in a series of clinical cases and judged to be useful. The method may limit unwanted deferral of the donor due to positivity in C4d Flow-PRA and/or FCXM and may be helpful in prediction of antibody mediated rejections. Furthermore, this method can provide information pretransplant in contrast to kidney biopsy and C4d evaluation done posttransplant.

CONCLUSIONS

We postulate that this method incorporates most of the features of all the available modalities (i.e., National Institute of Health-complement dependent lymphocytotoxicity, FCXM, cytotoxic FCXM and C4d-flowPRA) yet cost-effective and best suited for resource-limited laboratory/ies which is a common scenario in developing countries.