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Marginal zone B cells are critical to factor VIII inhibitor formation in mice with hemophilia A

Patricia E. Zerra, Courtney Cox, W. Hunter Baldwin, Seema R. Patel, Connie M. Arthur, Pete Lollar, Shannon L. Meeks and Sean R. Stowell

Key points

  • FVIII co-localizes with MZ B cells following infusion into hemophilia A mice.

  • Depletion of MZ B cells prevents FVIII inhibitor development in hemophilia A mice.

Abstract

While factor VIII (FVIII) replacement therapy can be life saving for patients with hemophilia A, neutralizing alloantibodies to FVIII, known as inhibitors, develop in a significant number of patients and actively block FVIII activity, making bleeding difficult to control and prevent. Although a variety of downstream immune factors likely regulate inhibitor formation, the identification and subsequent targeting of key initiators in inhibitor development may provide an attractive approach to prevent inhibitor formation before amplification of the FVIII immune response occurs. As the initial steps in FVIII inhibitor development remain incompletely understood, we sought to define early regulators of FVIII inhibitor formation. Our results demonstrate that FVIII localizes in the marginal sinus of the spleen of FVIII-deficient mice shortly after injection, with significant co-localization with marginal zone (MZ) B cells. FVIII not only colocalizes with MZ B cells, but specific removal of MZ B cells completely prevented inhibitor development following FVIII infusion. Subsequent re-challenge with FVIII following MZ B cell re-constitution resulted in a primary antibody response, demonstrating that MZ B cell depletion did not result in FVIII tolerance. While recipient exposure to the viral-like adjuvant poly I:C enhanced anti-FVIII antibody formation, MZ B cell depletion continued to display similar effectiveness in preventing inhibitor formation following FVIII infusion in this inflammatory setting. These data strongly suggest that MZ B cells play a critical role in initiating FVIII inhibitor formation and suggest a potential strategy to prevent anti-FVIII alloantibody formation in patients with hemophilia A.

  • Submitted May 5, 2017.
  • Accepted September 22, 2017.