A non–complement-fixing antibody to β2 glycoprotein I as a novel therapy for antiphospholipid syndrome

Abstract

Key Points• A recombinant antibody recognizing the D1 domain of b2 glycoprotein I induces fetal loss and clot formation in animal models.• The CH2-deleted antibody fails to activate complement and prevents the procoagulant and proabortive effects of patient antibodies.A single-chain fragment variable (scFv) recognizing b2-glycoprotein 1 (b2GPI) from humans and other species was isolated from a human phage display library and engineered to contain an IgG1 hinge-CH2-CH3 domain. The scFv-Fc directed against b2GPI domain I-induced thrombosis and fetal loss, thus mimicking the effect of antibodies from patients with antiphospholipid syndrome (APS). Complement is involved in the biological effect of anti-b2GPI scFv-Fc, as demonstrated by its ability to promote in vitro and in vivo complement deposition and the failure to induce vascular thrombosis in C6-deficient rats and fetal loss in C5-depleted mice. A critical role for complement was also supported by the inability of the CH2-deleted scFv-Fc to cause vessel occlusion and pregnancy failure. This antibody prevented the pathological effects of anti-b2GPI antibodies from APS patients and displaced b2GPI-bound patient antibodies. The CH2-deleted antibody represents an innovative approach potentially useful to treat APS patients refractory to standard therapy. (Blood. 2014;123(22):3478-3487)

Antibodies to Domain 4/5 (Dm4/5) of β2-Glycoprotein 1 (β2GP1) in different antiphospholipid (aPL) antibody profiles

“…Thus, individuals with lower IgG aβ2GP1 values (single positive group) show significantly higher anti Dm4/5 values compared to normal controls. This may indicate that single positivity for aβ2GPI is related to the presence of higher concentrations of aDm4/5 antibodies, rather than to the more pathogenic aDm1 antibodies [13], and thus single positivity for aβ2GPI confers a lower risk for thromboembolic events. Indeed, the presence of aDm4/5 was poorly related to thromboembolic events, as opposed to the presence of aDm1 antibodies.…”

Diagnosis and management of the antiphospholipid syndrome

“…101 Subsequently, it has been demonstrated that complement activation contributes to APLA mediated thrombosis in mice as demonstrated by the ability of C5 inhibitors to prevent thrombosis in animals receiving infusion of anti-β 2 GPI antibodies. 102–104 Complement activation by APLA leads to generation of the anaphylotoxin C5a, which recruits monocytes and neutrophils, activates endothelial cells and induces expression of tissue factor. 105, 106 However, while increased levels of complement activation products have been detected in patients with APS, these have not been demonstrated to correlate with thrombosis.…”

Critical Role and Therapeutic Control of the Lectin Pathway of Complement Activation in an Abortion-Prone Mouse Mating

“…Rabbit polyclonal Abs to human C1r cross-reacting with mouse C1r (Sigma, Italy) and to mouse C9 (kindly provided by Prof. M. Daha, Leiden, The Netherlands) were used to reveal deposition of C1r and C9 using FITC-labeled goat anti-rabbit IgG (Jackson Immunoresearch) as secondary Ab. C3 deposits were detected using FITC-conjugated goat F(ab9) 2 fragment to mouse C3 (Cappel UK) as previously described (26). All Abs were incubated at room temperature for 1 h to a final concentration of 5 mg/ml.…”