title: In vivo neutralization of a C2 domain-specific human anti-Factor VIII inhibitor by an anti-idiotypic antibody.
abstract: Factor VIII (FVIII) administration elicits specific inhibitory antibodies (Abs) in about 25% of patients with hemophilia A. The majority of such Abs reacts with FVIII C2 domain. mAbBO2C11 is a high-affinity human monoclonal antibody (mAb) directed toward the C2 domain, which is representative of a major class of human FVIII inhibitors. Anti-idiotypic Abs were raised to mAbBO2C11 to establish their neutralizing potential toward inhibitors. One mouse anti-idiotypic mAb, mAb14C12, specifically prevented mAbBO2C11 binding to FVIII C2 domain and fully neutralized mAbBO2C11 functional inhibitory properties. Modeling of the 3-D conformation of mAb14C12 VH and alignment with the 3-D structure of the C2 domain showed putative 31 surface-exposed amino acid residues either identical or homologous to the C2 domain. These included one C2 phospholipid-binding site, Leu2251-Leu2252, but not Met2199-Phe2200. Forty putative contact residues with mAbBO2C11 were identified. mAb14C12 dose-dependently neutralized mAbBO2C11 inhibitory activity in mice with hemophilia A reconstituted with human recombinant FVIII (rFVIII), allowing full expression of FVIII activity. It also neutralized in an immunoprecipitation assay approximately 50% of polyclonal anti-C2 Abs obtained from 3 of 6 unrelated patients. mAb14C12 is the first example of an anti-idiotypic Ab that fully restores FVIII activity in vivo in the presence of an anti-C2 inhibitor. The present results establish the in vitro and in vivo proof of concept for idiotype-mediated neutralization of a major class of FVIII inhibitors.
authors.affiliation: Center for Molecular and Vascular Biology, University of Leuven, Belgium. jeanguy.gilles@med.kuleuven.ac.be
authors.forename: Jean Guy G
authors.initials: JG
authors.lastname: Gilles
authors.forename: Sabrina C
authors.initials: SC
authors.lastname: Grailly
authors.forename: Marc
authors.initials: M
authors.lastname: De Maeyer
authors.forename: Marc G
authors.initials: MG
authors.lastname: Jacquemin
authors.forename: Luc P
authors.initials: LP
authors.lastname: VanderElst
authors.forename: Jean-Marie R
authors.initials: JM
authors.lastname: Saint-Remy
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology*; D000918:Antibody Specificity; D001666:Binding Sites, Antibody; D005167:Factor VII / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007930:Leucine; D008715:Methionine; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009500:Neutralization Tests; D010649:Phenylalanine; D010743:Phospholipids; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000276:immunology
chemical_list: D000888:Antibodies, Anti-Idiotypic; D010743:Phospholipids; D011994:Recombinant Proteins; D010649:Phenylalanine; D005167:Factor VII; D008715:Methionine; D007930:Leucine