Effects of rFVIIIFc on human macrophages

Immune responses in hemophilia A patients to replacement factor VIII can be either tolerogenic or immunogenic, the latter resulting in induction of non-neutralizing anti-factor VIII antibodies or neutralizing antibodies called inhibitors. Since these inhibitors render replacement FVIII treatment essentially ineffective, preventing or eliminating them are of top priority in disease management. The extended half-life recombinant factor VIII Fc fusion protein (rFVIIIFc) is an approved therapy for hemophilia A patients. In addition, it has been reported that rFVIIIFc can induce tolerance to FVIII in hemophilia A patients that have developed inhibitors. Given that the IgG1 Fc region has the potential to interact with immune cells expressing Fc receptors and thereby affect the immune response to rFVIII, we investigated how human macrophages, expressing both Fc receptors and receptors reported to bind FVIII, respond to rFVIIIFc. We show herein that rFVIIIFc, but not rFVIII, uniquely skews macrophages towards an alternatively activated regulatory phenotype. rFVIIIFc initiates signaling events that result in morphological changes, as well as a specific gene expression and metabolic profile that is characteristic of the regulatory type Mox/M2-like macrophages. Further, these changes are dependent on rFVIIIFc-Fc receptor interactions. Our findings elucidate mechanisms of potential immunomodulatory properties of rFVIIIFc. Human monocyte-derived macrophages (n=3) were treated with hIgG1, rFVIII or rFVIIIFc for 6h