Association of IgA-anti-Fab autoantibodies with disease stage in head-and-neck cancer

Pre-existing canine anti-IgG antibodies: implications for immunotherapy, immunogenicity testing and immunoassay analysis

One of the most enigmatic features of humoral immunity is the prevalent presence of circulating autoantibodies against IgG. These autoantibodies consist of several subsets, including rheumatoid factors, anti-Fab/anti-F(ab′)₂-autoantibodies, and anti-idiotypic antibodies. Anti-IgG autoantibodies can impair the safety and efficacy of therapeutic antibodies and interfere with immunogenicity tests in clinical trials. They can also cross-react with allospecific IgG, presenting as heterophilic antibodies that interfere with diagnostic immunoassays. Owing to these factors, recent years have seen a resurgent interest in anti-IgG autoantibodies, but their underlying clinical significance, as well as biological roles and origins, remain opaque. Increased knowledge about canine anti-IgG autoantibodies could facilitate the development of canine immunotherapies and help in understanding and counteracting immunoassay interference. This study investigated the clinical significance and interconnection of heterophilic antibodies, anti-Fab, and anti-F(ab′)₂-autoantibodies in dogs. We performed a 2-year prospective follow-up of dogs with heterophilic antibodies and analyzed serum for anti-Fab and anti-F(ab′)₂-autoantibodies. Canine heterophilic antibodies can persist for at least 2 years in serum. A widespread occurrence of anti-Fab and anti-F(ab′)₂-autoantibodies was found, with reactivity to cryptic epitopes in the IgG hinge region and sporadic cross-reactivity with mouse IgG. Canine anti-Fab and anti-F(ab′)₂-autoantibodies are thus potential sources of clinical immunogenicity and immunoassay interference.

IgG anti-hinge antibodies against IgG4 F(ab')2 fragments generated using pepsin are useful diagnostic markers for rheumatoid arthritis: implications of the possible roles of metalloproteinases and IgG subclasses in generating immunogenic hinge epitopes

Background

Pepsin agglutinators, discovered over 50 years ago, have been recently referred to as anti-hinge antibodies (AHAs) because of their reaction with the IgG hinge epitope. AHAs have different reactivity for each hinge epitope generated by each protease that cleaves the hinge region at different sites. Moreover, AHAs have different reactivity against different hinge epitopes derived from each IgG subclass even when the same protease is used. Since the expression of matrix metalloproteinase-3 (MMP-3) is enhanced in rheumatoid arthritis (RA), AHA production could also be increased. The purpose of this study was to determine whether the levels of AHAs against IgG hinge epitopes produced by MMP-3 are elevated in RA.

Methods

The serum levels of IgG or IgA AHAs against the IgG1/IgG4 F(ab’)₂ fragments, generated by either MMP-3 or pepsin, were measured using ELISA in 111 patients with RA and 81 healthy controls (HC). Receiver operating characteristic (ROC) analysis was used for obtaining optimal cutoff values and cutoff values indicating high specificity (> 95%) of the AHA. The targeted epitope of a specific AHA was investigated through inhibition ELISA.

Results

Seven AHAs were statistically higher in RA patients than in HC, except IgG AHA against IgG1 F(ab’)₂, which was generated by MMP-3 proteolytic cleavage. The areas under the ROC curve were 0.66–0.80, although the sensitivities at high specificity were low (5.4–24.3%). The cumulative number of positive AHAs in each individual was statistically higher in RA patients than in HC, suggesting the extreme extent of AHA repertoires in RA. Inhibition studies revealed that IgG AHAs against IgG4 F(ab’)₂ fragments generated by pepsin cross-reacted with IgG1 F(ab’)₂ fragments generated by pepsin. Multivariate logistic regression analysis identified the IgG AHA against IgG4 F(ab’)₂ fragments generated by pepsin as an independent variable for RA diagnosis, even in RA patients who were negative for both RF and ACPA (odds ratio 1.18, 95% CI 1.06–1.32; P = 0.003). Additional experiments using non-RA patients finally strengthened the diagnostic utility.

Conclusion

In RA patients, we observed diversification and amplification of AHA repertoires and diagnostic utility of the specific AHA against IgG4 F(ab’)₂ fragments generated by pepsin but not MMP-3.

A monoclonal antibody against hinge-cleaved IgG restores effector function to proteolytically-inactivated IgGs in vitro and in vivo

We report a chimeric monoclonal antibody (mAb) directed to a neo-epitope that is exposed in the IgG lower hinge following proteolytic cleavage. The mAb, designated 2095-2, displays specificity for IdeS-generated F(ab')₂ fragments, but not for full-length IgG or for closely-related F(ab')₂ fragments generated with other proteases. A critical component of the specificity is provided by the C-terminal amino acid of the epitope corresponding to gly-236 in the IgG1 (also IgG4) hinge. By its ability to bind to IdeS-cleaved anti-CD20 mAb, mAb 2095-2 fully restored antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against WIL2-S cells to the otherwise inactive anti-CD20 IgG1 F(ab')₂ fragment. Similarly, 2095-2 reinstated ADCC against MDA-MB-231 cells to an anti-CD142 IgG1 F(ab')₂ fragment. mAb 2095-2 was also capable of eliciting both CDC and ADCC to IgG4 F(ab')₂ fragments, an IgG subclass that has weaker ADCC and CDC when intact relative to intact IgG1. The in vitro cell-based efficacy of 2095-2 was extended to the in vivo setting using platelets as a cell clearance surrogate. In a canine model, the co-administration of 2095-2 together with IdeS-generated, platelet-targeting anti-CD41/61 F(ab')₂ fragment not only restored platelet clearance, but did so at a rate and extent of clearance that exceeded that of intact anti-CD41/61 IgG at comparable concentrations. To further explore this unexpected amplification effect, we conducted a rat study in which 2095-2 was administered at a series of doses in combination with a fixed dose of anti-CD41/61 F(ab')₂ fragments. Again, the combination, at ratios as low as 1:10 (w/w) 2095-2 to F(ab')₂, proved more effective than the anti-CD41/61 IgG1 alone. These findings suggest a novel mechanism for enhancing antibody-mediated cell-killing effector functions with potential applications in pathologic settings such as tumors and acute infections where protease activity is abundant.

Pretransplant serum IgA concentration and IgA-anti-Fab autoantibody activity as prognostic indicators of kidney graft survival

IgA concentration and IgA-anti-Fab autoantibody activity were tested in pretransplant sera of 308 kidney graft recipients. Recipients with a serum IgA concentration of 2 g/l or greater had a 1-year graft survival rate of 83%, compared with a 68% rate in recipients with serum IgA of less than 2 g/l (P < 0.005). Serum IgA concentration and IgA-anti-Fab autoantibody activity were significantly associated (r = 0.38, P < 0.0001). Recipients with a high pretransplant IgA-anti-Fab activity had a significantly better graft survival rate (81%) than patients with low pretransplant IgA-anti-Fab (67%, P < 0.025). When IgA-anti-Fab and serum IgA were considered together, 137 recipients with high IgA-anti-Fab and high serum IgA had a 86% 1-year graft survival rate, which was significantly better than the 63% survival rate in patients with low IgA-anti-Fab and low serum IgA (P < 0.0005). The pretransplant serum IgA level and IgA-anti-Fab autoantibody activity were excellent predictors of kidney graft outcome.

Graft-protective role of high pretransplantation IgA-anti-Fab autoantibodies: confirmatory evidence obtained in more than 4000 kidney transplants. The Collaborative Transplant Study

BACKGROUND

Preliminary studies showed an excellent success rate of kidney grafts in patients with high pretransplantation serum levels of IgA autoantibodies directed against the Fab region of the human IgG molecule.

METHODS

With the collaboration of 30 centers from around the world, we attempted to verify the role of IgA-anti-Fab autoantibodies in kidney transplantation in an entirely new series of 4316 cadaveric kidney transplants, with special consideration of presensitized and poorly HLA-matched recipients.

RESULTS

In agreement with previously published preliminary findings, 147 recipients with a high pretransplantation IgA-anti-Fab of >1000 had a 2-year kidney graft survival rate of 88+/-3% (+/- SE), compared with an 80+/-1% rate in 851 recipients with a low IgA-anti-Fab of <60 (P = 0.02). Even in patients at an increased risk of graft rejection, high pretransplantation IgA-anti-Fab autoantibody activity was associated with superior graft survival. Among 815 presensitized patients, 31 had a high pretransplantation IgA-anti-Fab activity of >1000 and their 2-year graft survival rate was 94+/-4%, in contrast to a 71+/-4% rate in 165 presensitized recipients with a low IgA-anti-Fab of <60 (P = 0.02). Of 2294 recipients who received a kidney with > or =3 HLA-A+B+DR mismatches, 79 recipients had a high pretransplantation IgA-anti-Fab of >1000 and a 2-year graft survival rate of 90+/-4%, as compared with a 79+/-2% rate in 459 patients with a low IgA-anti-Fab of <60 (P = 0.04).

CONCLUSIONS

The present study confirms that kidney graft recipients with high pretransplantation IgA-anti-Fab activity have excellent graft survival, and it extends this observation to presensitized recipients and poor HLA matches.

Does AIDS emerge from a disequilibrium between two complementary groups of molecules that mimic MHC?

There is increasing evidence that a disturbance of self-nonself-recognition plays an important role in the immunopathogenesis of AIDS. Here, Caner Susal, Volker Daniel and Gerhard Opelz speculate that the immune system is balanced between two groups of molecules that mimic major histocompatibility complex (MHC) proteins; AIDS is suggested to emerge as a consequence of human immunodeficiency virus (HIV) disturbing this balance in favor of anti-MHC class II responses.

The impact of elevated serum IgA and race on primary recipient renal allograft survival

This study correlated overall serum IgA levels in pretransplant (preTx) sera with graft survival. IgA levels, determined by nephelometry, were normally distributed, with a mean level of 255 +/- 139 mg/dl and a median of 234 mg/dl in 631 adult primary kidney allograft recipients and a mean level of 213 +/- 123 mg/dl with a median of 196 mg/dl for 100 retransplant recipients. Improved 3-year survival was associated with a high preTx IgA serum level in primary recipients (Kaplan-Meier analysis, P = 0.01), but not in retransplant patients. After stratifying by race, IgA correlated with graft survival in Caucasian, Hispanic, and "other" (Middle Eastern, Indian subcontinent, and Asian) primary recipients (P < or = 0.04), but not in African Americans. Higher survival rates were not associated with IgA in primary recipients stratified for rejection episodes, blood transfusions, or HLA-DR mismatches. Graft survival was improved in patients with > 2 HLA-AB mismatches and serum IgA above the median. PreTx IgA level and IgA alpha-HLA activity were significantly associated in preTx sera of primary renal allograft recipients (chi 2 = 7.145, P = 0.01), although only 9% (12/133) of sera tested displayed IgA anti-HLA class I reactivity. Thus, enhanced graft survival mediated by elevated serum IgA levels may due in part to competition for allograft HLA class I binding with deleterious Ig subclasses or immune effector cells. Elevated serum IgA may also reflect an altered immunoregulatory state. The results suggest that, depending on the racial group, preTx serum IgA levels are a prognostic indicator of graft survival in primary renal allograft recipients.