A Deletion Variant of Human Factor VIII Displaying Low Immunogenicity in a Murine Model of Hemophilia A

The therapeutic clotting factor VIII (FVIII) is known for its particular immunogenicity, with nearly 30% of hemophilic patients developing neutralizing antibodies against the infused protein. The root cause of this immunogenicity is still not well understood, but intrinsic factors, such as FVIII byproducts, have been linked to the immunological response elicited. Bioengineering of the FVIII molecule has been improving its recombinant (rhFVIII) production in many aspects, mainly enhancing its expression and stability. Assessment of immunogenicity for novel recombinant isoforms is crucial for further development and scaling-up processes, particularly due to the unpredictable antigenic properties and their impact on neutralizing antibody formation. In the present study, we describe a bioengineered human recombinant FVIII (rhFVIII-H6A), which induces lower immunogenicity in a murine model of hemophilia A. The rhFVIII-H6A product is characterized by a B-domain-deleted heavy chain (HCh), with the C-terminal of the B-domain fused to the light chain (BΔ-LCh). Compared to plasma-derived FVIII (pdFVIII) and rhFVIII reference products, treating hemophilic mice with rhFVIII-H6A induced lower levels of anti-FVIII antibody formation, including those with inhibitory neutralizing activity, while no difference was observed in the functional activity of rhFVIII-H6A in reverting the in vivo hemophilia phenotype. In addition, our results indicate that deleting the major part of the B-domain from the HCh might lower the immunogenicity of novel rhFVIII products.