Some, but not all, hemophilia A patients who receive factor VIII (FVIII) replacement therapy develop antibodies that interfere with FVIII coagulation activity (“inhibitors”), and their development is T-cell dependent. Immune tolerance induction protocols induce longterm tolerance to FVIII in a number of these patients, and although this clinical success is remarkable, its multifactorial molecular basis is still poorly understood. Our laboratory is characterizing protein-protein interactions and subsequent cytokine signaling that occurs when antigen-presenting cells present FVIII-derived peptides to T-cell receptors (TCRs). We previously mapped HLA-DR-restricted T-cell epitopes recognized by T cells from several related individuals with mild hemophilia A due to the missense substitution FVIIIA2201P (
three clones secreted IL-17 (20–600 pg/ml), relatively low levels of IFN-g and TNF-a (0–200 pg/ml) and no IL-4 or IL-10;
two clones secreted IL-4 and IL-10 (100–500 pg/ml), relatively low IFN-g and TNF-a (0–200 pg/ml) and no IL-17. In contrast, all six clones from the brother had a similar profile, secreting relatively high levels of IFN-g (500–1500 pg/ml), moderate levels of TNF-a, IL-4, and IL-10 (50–300 pg/ml) and no IL-17. These profiles indicate that FVIII-specific clones from the proband are of the Th17 and Th2 lineage, whereas the brother had a Th1high/Th2low T-cell response.
We next sequenced the TCRBV-D-J genes to investigate whether differences in the TCRs correlated with T-cell responses. Four distinct TCRBV-D-J sequences were identified among the 11 clones that correlated with the observed differences in cytokine secretion, suggesting a structural basis for these functional differences. Expression patterns of chemokine receptors considered to be markers of Th1, Th2, and Th17 cells provided additional evidence for the Th lineage designations of the clones. Eight additional clones were isolated from the proband 21 months following his peak inhibitor response, when his inhibitor titer was 5 Bethesda units/mL, and none of them secreted IL-17, suggesting Th17 cells may play a significant role in early stages of anti-FVIII antibody responses. The importance of Th17 cells in various inflammatory as well as autoimmune responses has been recognized only recently. This is the first report of Th17 involvement in epitope-specific T-cell responses to FVIII.
Disclosures: No relevant conflicts of interest to declare.