Regulation of immune responses to therapeutic factor VIII by transplacental delivery of Fc-fused immunodominant factor VIII domains or peptides.

Patients with severe hemophilia A (HA) often develop undesired immune responses to therapeutic factor VIII (FVIII) that hamper replacement therapy with FVIII-derived products. The transplacental delivery of two Fc-fused FVIII domains in pregnant HA mice was shown to induce partial FVIII-specific immune tolerance in the offspring. Here, we evaluated whether the transplacental delivery of Fc-fused FVIII (rFVIIIFc) induces complete immune tolerance towards FVIII.

Binding of therapeutic Fc-fused factor VIII to the neonatal Fc receptor at neutral pH associates with poor half-life extension.

Fusion of therapeutic proteins to the Fc fragment of human IgG1 promotes their FcRn-mediated recycling and subsequent extension in circulating half-life. However, different Fc-fused proteins, as well as antibodies with different variable domains but identical Fc, may differ in terms of extension in half-life. Here we compared the binding behaviour to FcRn of Fc-fused FVIII, Fc-fused FIX and two human monoclonal HIV-1 broadly-neutralizing IgG1, m66.