title: Measurement of serum levels of natalizumab, an immunoglobulin G4 therapeutic monoclonal antibody.
abstract: Human immunoglobulin G4 (IgG4) is a poor trigger of effector functions and, therefore, is the preferred subclass for therapeutic monoclonal antibodies that merely aim to block their in vivo targets. An example is natalizumab, a recombinant IgG4 antibody directed against α4-integrin and used for treatment of multiple sclerosis. Efficient treatment requires that the pharmacokinetics of therapeutic monoclonal antibodies can be accurately monitored. For natalizumab, this requires special precautions due to recently reported structural peculiarities of human IgG4. Here we describe the development of an assay to determine serum levels of natalizumab. Compared with other IgG subclasses, human IgG4 possesses unique structural properties that influence its interactions in both in vivo and in vitro settings. Thus, IgG4 undergoes Fab arm exchange in vivo, resulting in effectively monovalent antibodies. Furthermore, IgG4 is able to bind to other human and nonhuman IgG via Fc interactions. We demonstrate how these features can interfere with measurement of specific IgG4 and describe how we addressed these issues, resulting in an assay that is not sensitive to Fab arm exchange by natalizumab or to IgG4 Fc interactions.
authors.affiliation: Sanquin Research, 1066 CX Amsterdam, The Netherlands. t.rispens@sanquin.nl
authors.forename: Theo
authors.initials: T
authors.lastname: Rispens
authors.forename: Astrid van
authors.initials: Av
authors.lastname: Leeuwen
authors.forename: Anke
authors.initials: A
authors.lastname: Vennegoor
authors.forename: Joep
authors.initials: J
authors.lastname: Killestein
authors.forename: Rob C
authors.initials: RC
authors.lastname: Aalberse
authors.forename: Gerrit J
authors.initials: GJ
authors.lastname: Wolbink
authors.forename: Lucien A
authors.initials: LA
authors.lastname: Aarden
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000097:blood* / Q000737:chemistry; D061067:Antibodies, Monoclonal, Humanized; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000737:chemistry; D007074:Immunoglobulin G / Q000097:blood / Q000737:chemistry; D009103:Multiple Sclerosis / Q000188:drug therapy; D000069442:Natalizumab; D011485:Protein Binding; D011817:Rabbits
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D000069442:Natalizumab