Inhibitory antibodies to factor VIII (fVIII) develop in approximately 30% of patients with severe hemophilia A in response to infusions of fVIII. Inhibitor development is associated with a lower quality of life and an increased economic burden and is currently is considered the most significant complication of the management of hemophilia A. Additionally, factor VIII inhibitors can occur in nonhemophiliacs, i.e. acquired hemophilia A, in which there can be life and limb- threatening complications. Patients with severe hemophilia A have no circulating fVIII protein and thus normal recognition of fVIII as "self" does not develop. Accordingly, the therapeutic replacement fVIII protein is seen as "foreign" by the immune system. Given that fVIII is an immunologically foreign protein, it may not seem surprising that an antibody response to fVIII would occur. However, in both rodents and humans, intravenous injection of soluble proteins usually fails to induce immunity and often induces a tolerogenic state. For this reason, the substantial immunogenicity of fVIII is unexpected. The central question of this grant is why, and by what mechanism, does fVIII induce an immune response. There are 3 Specific Aims in this proposal.
In Aim 1, the role of the physiological site of fVIII presentation to the immune system, i.e. a site of inflammation where a clot is forming and where fVIII is released from its large carrier protein von Willebrand factor, will be characterized by comparing the immunogenicity of fVIII with an inactive form of fVIII in a murine hemophilia A immunogenicity model.
In Aim 2, a novel fVIII molecule (HOVA) will be constructed that has a well characterized T cell epitope of ovalbumin inserted into the B domain. A wide array of immunologic reagents specific for this T cell epitope, including tetramer reagents and TCR transgenic mice, are available to investigate the mechanism of CD4+ T cell response to intravenous infusion of HOVA. There is evidence that early exposure to fVIII at the time of a "danger signal" such as surgery or a major bleed increases the risk of antibody development.
In Aim 3 the role of toll like receptor activation on fVIII immunity will be addressed by comparing the CD4+ T cell response to intravenous infusion of HOVA as well as the ultimate antibody production in the presence and absence of toll like receptor agonists. The results of these experiments will allow for a deeper understanding of the substantial immunogenicity of fVIII and might provide insights for future design of novel fVIII molecules with decreased immunogenicity. This research plan along with the formal coursework and structured mentorship laid out in this proposal should provide the candidate with the training necessary to establish her as an independent investigator.

Public Health Relevance

Patients with hemophilia A have a deficiency in the blood coagulation protein factor VIII. Some patients with hemophilia A develop antibodies to factor VIII that worsens their bleeding problems and makes therapy difficult and expensive. In this project, we will develop a better understanding of the immune response to the factor VIII protein, which may lead to better treatment alternatives.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Clinical Investigator Award (CIA) (K08)
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Special Emphasis Panel (ZHL1-CSR-U (F1))
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Sarkar, Rita
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Emory University
Schools of Medicine
United States
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Nguyen, Phuong-Cac T; Lewis, Kenneth B; Ettinger, Ruth A et al. (2014) High-resolution mapping of epitopes on the C2 domain of factor VIII by analysis of point mutants using surface plasmon resonance. Blood 123:2732-9
Walter, Justin D; Werther, Rachel A; Polozova, Maria S et al. (2013) Characterization and solution structure of the factor VIII C2 domain in a ternary complex with classical and non-classical inhibitor antibodies. J Biol Chem 288:9905-14
Markovitz, Rebecca C; Healey, John F; Parker, Ernest T et al. (2013) The diversity of the immune response to the A2 domain of human factor VIII. Blood 121:2785-95
Summers, Ryan J; Meeks, Shannon L; Healey, John F et al. (2011) Factor VIII A3 domain substitution N1922S results in hemophilia A due to domain-specific misfolding and hyposecretion of functional protein. Blood 117:3190-8