Characterization of a factor VIII/immunoglobulin heavy chain μ double-knockout mouse model of hemophilia A for long-term exposure to factor VIII proteins.

Background: Deficiency of coagulation factor (F)VIII is the key characteristic of hemophilia A. The FVIII knockout mouse model is a valuable tool for investigating disease mechanisms and evaluating the pharmacokinetics (PK) and efficacy of therapeutic agents. However, its utility for long-term studies, particularly those focused on prophylaxis, is limited by the development of anti-FVIII antibodies following repeated FVIII administration. Objectives: To develop a FVIII knockout model that does not generate antibodies against FVIII but is not severely immunosuppressed. Methods: Established FVIII single-knockout (FVIII Results: DKO mice did not develop detectable anti-FVIII antibodies. The formation of FVIII-specific antibody-secreting cells was abrogated, and the presence of FVIII-specific T cells was substantially reduced. PK analysis performed after 3 weeks of FVIII exposure showed variable reductions in FVIII recovery and half-life in SKO mice. In contrast, PK parameters in DKO mice remained consistently within the expected physiological range. Conclusion: The DKO mouse model can be used for long-term studies of FVIII products and other hemostatic proteins, enabling the evaluation of repeated-dose PK and prophylactic efficacy without interference from inhibitor formation.