title: Dangerous liaisons: how the immune system deals with factor VIII.
abstract: Only a fraction of patients with hemophilia A develop a neutralizing antibody (inhibitor) response to therapeutic infusions of factor VIII. Our present understanding of the underlying causes of the immunogenicity of this protein is limited. In the past few years, insights into the uptake and processing of FVIII by antigen-presenting cells (APCs) have expanded significantly. Although the mechanism of endocytosis remains unclear, current data indicate that FVIII enters APCs via its C1 domain. Its subsequent processing within endolysosomes allows for presentation of a heterogeneous collection of FVIII-derived peptides on major histocompatibility complex (MHC) class II, and this peptide-MHC class II complex may then be recognized by cognate effector CD4(+) T cells, leading to anti-FVIII antibody production. Here we aim to summarize recent knowledge gained about FVIII processing and presentation by APCs, as well as the diversity of the FVIII-specific T-cell repertoire in mice and humans. Moreover, we discuss possible factors that can drive FVIII immunogenicity. We believe that increasing understanding of the immune recognition of FVIII and the cellular mechanisms of anti-FVIII antibody production will lead to novel therapeutic approaches to prevent inhibitor formation in patients with hemophilia A.
authors.affiliation: Department of Plasma Proteins, Sanquin-AMC Landsteiner Laboratory and van Creveld Laboratory, Amsterdam, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Wroblewska
authors.forename: B M
authors.initials: BM
authors.lastname: Reipert
authors.forename: K P
authors.initials: KP
authors.lastname: Pratt
authors.forename: J
authors.initials: J
authors.lastname: Voorberg
mesh_terms: D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood*; D000938:Antigen-Presenting Cells / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D003029:Coagulants / Q000008:administration & dosage / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D004705:Endocytosis; D000939:Epitopes; D005169:Factor VIII / Q000008:administration & dosage / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D006467:Hemophilia A / Q000097:blood / Q000188:drug therapy* / Q000276:immunology; D006801:Humans; D008213:Lymphocyte Activation; D008958:Models, Molecular; D011487:Protein Conformation; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D057134:Antibodies, Neutralizing; D003029:Coagulants; D000939:Epitopes; D014841:von Willebrand Factor; C078147:F8 protein, human; D005169:Factor VIII