Significance of C1q-fixing Donor-Specific Antibodies After Kidney Transplantation

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.

Approaches for the characterization of clinically relevant pre-transplant human leucocyte antigen (HLA) antibodies in solid organ transplant patients

The avoidance of antibody-mediated rejection (AMR) attributed to human leucocyte antigen (HLA) antibody incompatibility remains an essential function of clinical Histocompatibility and Immunogenetics (H&I) laboratories who are supporting solid organ transplantation. Developments in HLA antibody identification assays over the past thirty years have greatly reduced unexpected positive cellular crossmatches and improved solid organ transplant outcomes. For sensitized patients, the decision to register unacceptable HLA antigen mismatches is often heavily influenced by results from solid phase antibody assays, particularly the Luminex^® Single Antigen Bead (SAB) assays, although the clinical relevance of antibodies identified solely by these assays remains unclear. As such, the identification of non-clinically relevant antibodies may proportionally increase the number of unacceptable transplant mismatches registered, with an associated increase in waiting time for a compatible organ. We reflect on the clinical relevance of antibodies identified solely by the Luminex SAB^® assays and consider whether the application of additional assays and/or tools could further develop our ability to define the clinical relevance of antibodies identified in patient sera. Improvements in this area would assist equity of access to a compatible transplant for highly sensitized patients awaiting a solid organ transplant.

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.

Characteristics of Immunoglobulin M Type Antibodies of Different Origins from the Immunologic and Clinical Viewpoints and Their Application in Controlling Antibody-Mediated Allograft Rejection

Antibody-mediated allograft rejection (AMR) hinders patient prognosis after organ transplantation. Current studies concerning AMR have mainly focused on the diagnostic value of immunoglobulin G (IgG)-type donor-specific antihuman leukocyte antigen antibodies (DSAs), primarily because of their antigen specificity, whereas the clinical significance of immunoglobulin M (IgM)-type DSAs has not been thoroughly investigated in the context of organ transplantation because of their nonspecificity against antigens. Although consensus regarding the clinical significance and role of IgM antibodies is not clear, as discussed in this review, recent findings strongly suggest that they also have a huge potential in novel diagnostic as well as therapeutic application for the prevention of AMR. Most serum IgM antibodies are known to comprise natural antibodies with low affinity toward antigens, and this is derived from B-1 cells (innate B cells). However, some of the serum IgM-type antibodies reportedly also produced by B-2 cells (conventional B cells). The latter are known to have a high affinity for donor-specific antigens. In this review, we initially discuss how IgM-type antibodies of different origins participate in the pathology of various diseases, directly or through cell surface receptors, complement activation, or cytokine production. Then, we discuss the clinical applicability of B-1 and B-2 cell-derived IgM-type antibodies for controlling AMR with reference to the involvement of IgM antibodies in various pathological conditions.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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 factor and T-cell interactions during alloimmune inflammation in transplantation

Complement factor and T-cell signaling during an effective alloimmune response plays a key role in transplant-associated injury, which leads to the progression of chronic rejection (CR). During an alloimmune response, activated complement factors (C3a and C5a) bind to their corresponding receptors (C3aR and C5aR) on a number of lymphocytes, including T-regulatory cells (Tregs), and these cell-molecular interactions have been vital to modulate an effective immune response to/from Th1-effector cell and Treg activities, which result in massive inflammation, microvascular impairments, and fibrotic remodeling. Involvement of the complement-mediated cell signaling during transplantation signifies a crucial role of complement components as a key therapeutic switch to regulate ongoing inflammatory state, and further to avoid the progression of CR of the transplanted organ. This review highlights the role of complement-T cell interactions, and how these interactions shunt the effector immune response during alloimmune inflammation in transplantation, which could be a novel therapeutic tool to protect a transplanted organ and avoid progression of CR.

Clinical Outcome of Patients With De Novo C1q-Binding Donor-Specific HLA Antibodies After Renal Transplantation

BACKGROUND

De novo donor specific anti-HLA antibodies (dnDSA) may cause graft loss in renal transplant recipients. The capability to bind the complement may help to stratify the risk for inferior outcomes associated with dnDSA. We developed a modified C1q-binding assay and hypothesized that C1q-binding dnDSA could differentiate between indolent and harmful dnDSA causing antibody-mediated rejection (AMR) and graft loss.

METHODS

We retrospectively identified 59 renal transplant recipients who developed dnDSA and had serum available and complete follow-up. All patients were analyzed for C1q-binding dnDSA at the time of dnDSA detection, and 1-year later or at time of AMR. AMR-positive patients were also tested 6 to 12 months before the event if IgG dnDSA was present.

RESULTS

Thirty-seven of 59 dnDSA patients developed AMR during 5.9 ± 3.1 years follow-up. AMR-positive patients had more dnDSA with a significant higher frequency of class I, a higher frequency and a higher mean fluorescence intensity value of C1q-dnDSA at all time-points. Death-censored AMR-free and allograft survivals were significantly lower in C1q-dnDSA patients. In multivariate analysis, C1q-dnDSA was an independent risk factor for AMR.

CONCLUSIONS

C1q-binding dnDSA is associated with inferior outcomes, yet not in all patients. Nevertheless, C1q-dnDSA was shown to be an independent risk factor of AMR and graft loss and may be a useful tool to stratify the immunological risk for AMR.

Relationship between Mean Fluorescence Intensity and C1q/C3d-fixing capacities of anti-HLA antibodies

BACKGROUND

Complement-binding assays are proposed to better stratify the risk of antibody-mediated rejection associated-graft failure. Despite promising clinical results, some have suggested that the MFI of anti-HLA antibodies may influence these tests.

METHODS

We investigated the impact of Abs MFI reduction, induced by plasmapheresis, on C1q- and C3d-binding assays. Sera provided from 7 sensitized kidney transplant patients were analyzed.

RESULTS

Four hundreds and thirty-three SABs were analyzed. Before plasmapheresis, when compared to C1q- SABs, C1q+ SABs had a higher median MFI [17397 (IQR: 14851-18794) vs. 2745 (IQR: 1125-6476), p<0.01]. SABs that remained C1q+ after plasmapheresis had a higher median MFI. Regarding the C3d assay, results were strictly comparable. MFI value was a powerful predictor of both C1q and C3d positivity [AUC 0.97 (CI95% 0.95-0.99) and 0.96, (CI95% 0.93-0.98), respectively].

CONCLUSION

Our data suggest that both C1q- and C3d-binding assays are intimately linked to the MFI of anti-HLA Abs.

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

BACKGROUND

Kidney 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.

METHODS

This 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.

RESULTS

C1q-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).

CONCLUSION

C1q-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.

Kidney Transplantation With Ultralong-Term (42 Years) Survival of a 100-Year-Old Graft

BACKGROUND

In kidney transplantation, long-term graft survival has improved over the last few decades. Study to understand ultralong-term graft survival with graft functioning is rare, but a few researchers have tried to explain the factors involved in long-term graft survival. In this report, we explore the predictive factors that can be involved in ultralong-term graft survival.

MATERIAL AND METHODS

Immunologic evaluations of the patients were performed using crossmatch (XM), serological, and high-resolution HLA typing for 8 loci. A transplant recipient was treated with azathioprine as immunosuppressive monotherapy for 42 years. Donor-specific antibodies (DSAs) were identified using panel reactive antibody single antigen beads (PRA-SAB) followed by EpVix and Matchmaker epitope analysis to define the immunogenic mismatch eplets.

RESULTS

The patient and donor were haploidentical for 7 loci and identical at the HLA-DPA1* locus. Among 61 identified eplet mismatches, DSAs were not detected against 59 eplets after 42 years of exposure to the patient's immune system with the exceptions of antibodies against the public eplets 9Y and 9YL from allele HLA-DPB1*03:01, and the transplanted kidney exhibited preserved structures.

CONCLUSION

The transplanted kidney has the preserved structure based on magnetic resonance imaging, the 2 DSAs were not deleterious to the graft until now, and the eplet mismatches were considered acceptable. The patient is in good clinical condition living with a 100-year-old graft, a serum creatinine level of 1.5 mg/dL, and an estimated glomerular filtration rate of 50 mL/1.72 m².

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

BACKGROUND

C1q-binding donor-specific antibody (DSA) is detrimental to transplanted kidney function. However, the factors that affect C1q binding status are unclear.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Relationship among C1q-fixing de novo donor specific antibodies, C4d deposition and renal outcome in transplant glomerulopathy

BACKGROUND

The C1q-binding properties of donor specific antibodies (DSA) may be related to antibody-mediated rejection and poor outcome.

METHODS

We retrospectively studied 35 kidney transplant recipients with transplant glomerulopathy (TG) and de novo DSA (dnDSA). C1q dnDSA were measured in the serum stored at renal biopsy and the association among C1q-fixing dnDSA, C4d deposition and graft loss was examined.

RESULTS

Of the 35 patients with dnDSA and TG, 15 (42.9%) had C1q-positive dnDSA and 20 (57.1%) had C1q-negative dnDSA. Ten out of 15 patients with C1q-positive dnDSA (66.6%) and 5 with C1q-negative dnDSA (25%) had C4d positive staining renal biopsies (P=0.02), being the C1q-negative dnDSA/C4d-negative TG 42.9% of the total. The C1q-positive dnDSA group has significantly higher IgG DSA Class II MFI than the C1q-negative dnDSA group (P=0.004). Patients with C4d deposits have significantly higher IgG DSA MFI for both Class I and Class II than those without C4d deposits (P=0.02). We found a trend toward higher graft loss in the C1q-positive dnDSA group (60%) versus the C1q-negative dnDSA group (40%) without a statistical significance (P=0.31).

CONCLUSION

Our study provides further characterization of TG associated with dnDSA. The major part of dnDSA-associated TG was C1q-negative and the presence of C1q-fixing dnDSA did not significantly correlate with graft outcome.

Influence of de novo donor-specific antibody on early renal allograft function recovery

BACKGROUND

The aim of the present study is to investigate the impact of de novo donor-specific antibodies (dnDSA) on early graft function, to provide objective reference for early clinical diagnosis and reasonable individualized treatment.

METHODS

305 cases of renal transplant patients for the first time were observed in this study. Follow-up time for all recipients was 6 months after operation. HLA antibody, DSA, renal function were monitored after transplant.

RESULTS

In total of 305 cases, 66 cases (21.64%) were HLA antibody positive and 21 cases (6.89%) showed acute rejection (AR) in 6 months after transplant. The HLA antibody-positive patients included six cases of dnDSA-positive and 60 cases of dnDSA-negative. The incidence of AR was 2.09% (5/239) in HLA antibody-negative patients, 18.33% (11/60) in HLA antibody positive with DSA-negative patients, and 83.33% (5/6) in HLA antibody-positive patients with DSA-positive. There was a big difference between DSA-negative and DSA-positive patients (p < 0.01). The recovery time of AR patients with DSA-positive were longer than DSA-negative patients, and the recovery graft function of AR patient with DSA-positive were not as good as those with DSA-negative.

CONCLUSIONS

The appearance of dnDSA in the early stage of kidney transplantation is a warning sign of AR occurrence. Dynamic monitoring of HLA antibody and DSA could predict the state of graft function, and play an important role in the prevention of AR, timely and effectively.