The C1 and C2 domains of blood coagulation factor VIII mediate itsendocytosis by dendritic cells

摘要

The development of inhibitory antibodies to therapeutic factor VIII is the majorcomplication of replacement therapy in patients with hemophilia A. The firststep in the initiation of the anti-factor VIII immune response is factor VIIIinteraction with receptor(s) on antigen-presenting cells, followed byendocytosis and presentation to na?ve CD4~(+) T cells. Recentstudies indicate a role for the C1 domain in factor VIII uptake. We investigatedwhether charged residues in the C2 domain participate in immunogenic factor VIIIuptake. Co-incubation of factor VIII with BO2C11, a monoclonal C2-specificimmunoglobulin G, reduced factor VIII endocytosis by dendritic cells andpresentation to CD4~(+) T cells, and diminished factor VIIIimmunogenicity in factor VIII-deficient mice. The mutation of basic residueswithin the BO2C11 epitope of C2 replicated reduced in vitro immunogenic uptake, but failed to prevent factor VIII immunogenicity in mice.BO2C11 prevents factor VIII binding to von Willebrand factor, thus potentiallybiasing factor VIII immunogenicity by perturbing its half-life. Interestingly, afactor VIII~(Y1680C) mutant, that does not bind von Willebrand factor,demonstrated unaltered endocytosis by dendritic cells as well as immunogenicityin factor VIII-deficient mice. Co-incubation of factor VIII~(Y1680C)with BO2C11, however, resulted in decreased factor VIII immunogenicity in vivo . In addition, a previously described triple C1mutant showed decreased uptake in vitro , and reducedimmunogenicity in vivo , but only in the absence of endogenousvon Willebrand factor. Taken together, the results indicate that residues in theC1 and/or C2 domains of factor VIII are implicated in immunogenic factor VIIIuptake, at least in vitro . Conversely, invivo , the binding to endogenous von Willebrand factor masks thereducing effect of mutations in the C domains on factor VIII immunogenicity.