Detection of Factor VIII-Specific Memory B Cells in Patients with Hemophilia A and Factor VIII Inhibitors

Abstract

The development of neutralizing anti-FVIII antibodies (FVIII inhibitors) in about 25% of patients with severe hemophilia A is the most serious complication in the treatment of hemophilia A patients with FVIII products. Little information is available on the immunological mechanisms that regulate the development and maintenance of FVIII inhibitors in patients.

Memory B cells are a central component of humoral immunity. They drive the rapid anamnestic antibody response that occurs after re-exposure to antigen and seem to be important for replenishing the pool of long-lived plasma cells to maintain long-term antibody levels in the absence of antigen. Nothing is known about the significance of FVIII-specific memory B cells in patients with hemophilia A who develop FVIII inhibitors. Therefore, we developed a new method to track FVIII-specific memory B cells in the blood of hemophilia A patients.

So far, we have analyzed 12 patients with hemophilia A (age: 8–43 years). Six of these patients were found to be positive and 6 negative for FVIII inhibitors. For comparison, we analyzed 12 healthy volunteers (age: 27–49 years). 1 out of 6 patients with inhibitors but none of the patients without inhibitors and none of the healthy volunteers had detectable FVIII-specific memory B cells in their peripheral blood. The detection limit for FVIII-specific memory B cells in patients with inhibitors was between 0.02% and 0.28% compared to total IgG memory B cells. Current activities focus on further advancing the technology with the aim to improve the detection limit for the detection of FVIII-specific memory B cells.