Examining Anti-Factor VIII IgM in Propagation of the Immune Response to Factor VIII in Hemophilia A

/Abstract Anti-factor VIII (FVIII) alloantibodies, known as inhibitors, develop in 20-30% of patients with severe hemophilia A following therapy with FVIII infusion. This, in turn, makes bleeding difficult to control and prevent, resulting in increased morbidity and mortality, increased cost of care and decreased quality of life. Despite the negative consequences of inhibitor formation, no prophylactic therapy is currently available to predict or prevent inhibitor development. This largely stems from a fundamental lack of understanding regarding key immune pathways that initiate this process. In order to effectively understand risk factors that may predict the likelihood of inhibitor development and then prevent this process in at-risk patients, our long-term goal is to identify the immunologic mechanisms that initiate and then orchestrate inhibitor formation, in order to predict and then prevent the development of anti-FVIII alloantibodies in patients with hemophilia A. This is in line with a key priority identified by the NHLBI to identify central immune targets that may be used to prevent inhibitor formation. Addressing these pertinent clinical problems, our data in a pre-clinical model shows that both marginal zone B cells (MZ B cells) and CD4 T cells are required for FVIII inhibitor formation. Interestingly, FVIII fails to induce CD4 T cell proliferation or IgG antibody production following a single FVIII exposure. Instead, we found that ant-FVIII IgM, which forms following the first exposure to FVIII and increases with subsequent exposures, facilitates IgG antibody formation and CD4 T cell proliferation. Our central hypothesis moving forward is that upon exposure to FVIII, MZ B cells generate a polyclonal anti-FVIII IgM response, leading to immune complex formation, enhanced presentation of antigen by dendritic cells, and CD4 T cell activation. Using a pre-clinical model, we first aim to elucidate the immune populations responsible for anti-FVIII IgM production, with the hypothesis that MZ B cells and dendritic cells play a central role. We will next examine the impact of anti-FVIII IgM on FVIII localization and uptake by antigen presenting cells in the spleen. Moreover, laboratory protocols for isolation of polyclonal and monoclonal anti-FVIII IgM antibodies will be further developed, allowing evaluation of the influence of antibody epitope specificity and clonality on the immune events influencing IgM- driven CD4 T cell proliferation. Completion of the outlined research will provide vital preliminary data for the successful submission of an independent R01 application, which will focus on elucidating specific mechanisms underlying IgM-driven CD4 T cell proliferation in FVIII inhibitor formation. These studies possess the capacity to not only provide new insight into key aspects of inhibitor formation, but may also provide an important framework to develop rational approaches to prophylactically prevent inhibitor development in patients with hemophilia A. Thus, completion of the outlined research will facilitate successful advancement to a career as an independent physician scientist, combining the care of pediatric hematology patients with continued advancements in the field. Project Number: 1R03HL178876-01 | Fiscal Year: 2025 | NIH Institute/Center: National Heart Lung and Blood Institute (NHLBI) | Principal Investigator: Patricia Zerra | Institution: EMORY UNIVERSITY, ATLANTA, GA | Award Amount: $234,750 | Activity Code: R03 | Study Section: Special Emphasis Panel[ZHL1 CSR-Q (J1)] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R03HL17887601