Anti-HLA Donor-Specific IgG Subclasses and C1q-binding Evolution in Posttransplant Monitoring

Abstract

BackgroundThe identification of low-level antibodies by single-antigen bead methodology has brought advancements to risk evaluation of kidney transplant recipients. However, the use of mean fluorescence intensity (MFI) to quantify antibodies and to guide therapy is not enough. Notably, immunoglobulin G (IgG) subclass switching is hypothesized to follow a programmed sequence after an emergency signal from the germinal center. In transplantation this process is not clear yet. In the present study, we sequentially evaluate anti-HLA donor specific antibody (DSA) subclasses, their profile changes, and C1q-binding ability and the influence of those characteristics on antibody mediated rejection (AMR) occurrence and allograft function.MethodsA total of 30 DSA-positive patients were tested for IgG subclass content and C1q-binding in sequential serum samples.ResultsTwenty-one patients were DSA-positive before transplant; patients sensitized only by transfusion or pregnancies had IgG1 and/or IgG3, and patients sensitized by both transfusion and pregnancies or previous transplant showed a broader range of IgG subclasses. C1q binding was detected in high MFI made up of IgG1 or multiple IgG subclasses. Only 4 patients were positive for C1q posttransplantation and 3 of these showed an increase in MFI, changes in subclasses patterns, AMR, and allograft dysfunction.ConclusionsPosttransplant evaluation of DSA subclasses and the ability to bind C1q may be informative for both AMR occurrence and allograft dysfunction. Monitoring these events may help to better define risk and interventional time points.

Characterization of the C1q-Binding Ability and the IgG1-4 Subclass Profile of Preformed Anti-HLA Antibodies by Solid-Phase Assays

“…Hence, high titers of strong C1q-binding subclasses, particularly IgG1, alone or combined with other IgG subclasses, mainly IgG2, may compose the hexamer formation to efficiently recruit the C1q protein. These results are in line with those recently reported by Ponsirenas et al (46), who, although without revealing the real-strength of IgG subclasses diluting serum-samples, found that C1q-binding was detected in high MFI antibodies comprised of IgG1 or multiple IgG subclasses. Only under certain conditions such as increased concentration of immunoglobulin, even IgG2 could effectively activate the complement (30).…”

Sensitization in transplantation: Assessment of risk (STAR) 2019 Working Group Meeting Report

“…However, these assays do not distinguish between stronger complement‐fixing IgG1 and IgG3 subclasses from the lesser complement‐fixing IgG2 and IgG4, given that the detection reagent is specific for all Fcγ. Different routes of allosensitization trigger distinct patterns of IgG subclasses directed against HLA 33‐35 . Preliminary studies of HLA antibody subclasses suggest that IgG2 and IgG4 do not constitute a large proportion of HLA DSAs.…”

“…Different routes of allosensitization trigger distinct patterns of IgG subclasses directed against HLA. [33][34][35] subclasses suggest that IgG2 and IgG4 do not constitute a large proportion of HLA DSAs. Rather, HLA IgG1 and IgG3 are the predominant subclasses associated with graft rejection and graft loss.…”

Understanding and using AlloSure donor derived cell-free DNA

“…This stratification and classification of DSA can be even further enhanced by DSA sub-typing as some classes of antibody are more efficient at fixing complement than others (Zhang 2018 ). C1q binding donor-specific antibodies are closely associated with acute ABMR, more severe graft injuries, and early graft failure, whereas C1q nonbinding donor-specific antibodies correlate with subclinical or chronic ABMR and late graft loss (Ponsirenas et al 2018 ).…”