Epitope localization of anti-factor VIII monoclonal antibodies determined by recombinant peptides.

In order to define the epitopes recognized by anti-coagulation factor VIII (FVIII) monoclonal antibodies, we have constructed a recombinant DNA epitope library from random fragments of the FVIII cDNA. The characterization of 33 different clones producing recombinant antigens in the expression vector, lambda gt11, has identified the epitopes for six different anti-FVIII monoclonal antibodies. The antigenic determinant for each antibody was defined by the overlapping or shared DNA sequence of multiple-immunoreactive clones. One weak inhibitor of FVIII coagulant activity binds within the gly701-ser750 sequence of the FVIII sequence. An antibody which recognizes the amino-terminus of FVIII heavy-chain (within trp14-tyr46) does not inhibit FVIII activity. Two non-neutralizing antibodies both map within residues asp807-ser817, while two other non-neutralizing antibodies bind within lys1673-pro1688. The general usefulness of this strategy for mapping FVIII antigenic determinants is discussed.