title: Antibody affinity maturation in vitro using unconjugated peptide antigen.
abstract: Selection of antibody library in vitro is almost always performed on a certain solid-phase with immobilized antigen. However, for the selection of small molecule binders, conjugation of the antigen to a carrier molecule is indispensable, which often leads to the selection of unwanted binders such as conjugate-binders or those with insufficient specificity. Here we describe a rapid and efficient way to improve the affinity of an anti-small molecule antibody without antigen derivatization. The method is based on the open-sandwich (OS) principle, which utilizes the antigen-dependent stabilization of antibody variable domain Fv. We used an anti-osteocalcin C-terminal peptide Fv that showed a good response but with moderate sensitivity in OS ELISA as a model. By selecting PCR-randomized V(H)-displaying phages for superior binders to the immobilized V(L) fragment in the presence of limited amount of antigen peptide, V(H) mutants that show superior detection sensitivity in OS ELISA were obtained, and were characterized to retain improved antigen-binding affinity. Furthermore, saturation mutagenesis of a mutant resulted in further improvement in sensitivity. This 'OS-selection' will be the first to select anti-small molecule antibodies without using conjugated antigens, and especially useful in the affinity maturation of antibodies whose Fv has limited stability in the absence of antigen.
authors.affiliation: Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, Tokyo, Japan.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Iwai
authors.forename: Bengü
authors.initials: B
authors.lastname: Oztürk
authors.forename: Masaki
authors.initials: M
authors.lastname: Ihara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ueda
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000915:Antibody Affinity; D000941:Antigens / Q000737:chemistry* / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007147:Immunoglobulin Light Chains / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007135:Immunoglobulin Variable Region / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry / Q000276:immunology*; D016133:Polymerase Chain Reaction; D015202:Protein Engineering / Q000379:methods
chemical_list: D000911:Antibodies, Monoclonal; D000941:Antigens; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D007135:Immunoglobulin Variable Region; D019151:Peptide Library; D010455:Peptides