ABSTRACT
Antibody engineering provides an excellent tool for the generation of human immunotherapeutics for the targeted treatment of solid tumours. We have engineered and selected a completely human antibody to epithelial glycoprotein-2 (EGP-2), a transmembrane glycoprotein present on virtually all human simple epithelia and abundantly expressed on a variety of human carcinomas. We chose to use the procedure of "guided selection" to rebuild a high-affinity murine antibody into a human antibody, using two consecutive rounds of variable domain shuffling and phage library selection. As a starting antibody, the murine antibody MOC-31 was used. After the first round of guided selection, where the V(H) of MOC-31 was combined in Fab format with a human V(L)C(L) library, a small panel of human light chains was identified, originating from a segment of the VkappaIII family, whereas the MOC-31 V(L) is more homologous to the VkappaII family. Nevertheless, one of the chimaeric Fabs, C3, displayed an off-rate similar to MOC-31 scFv. Combining the V(L) of C3 with a human V(H) library, while retaining the V(H) CDR3 of MOC-31, clones were selected using human V(H) genes originating from the rarely used V(H)7 family. The best clone, 9E, shows over 13 amino acid mutations from the germline sequence, has an off-rate comparable to the original antibody and specifically binds to the "MOC-31"-epitope on EGP-2 in specificity and competition ELISA, FACS analysis and immunohistochemistry. In both V(L) and V(H) of antibody 9E, three germline mutations were found creating the MOC-31 homologue residue. Structural modelling of both murine and human antibodies reveals that one of the germline mutations, 53Y in V(H) CDR2, is likely to be involved in antigen binding. We conclude that, although they may bind the same epitope and have similar binding affinity to the antigen as the original murine antibody, human antibodies derived by guided selection unlike CDR-grafted antibodies, may retain only some of the original key elements of the binding site chemistry. The selected human anti-EGP-2 antibody will be a suitable reagent for tumour targeting.
Subject(s)
Antibodies, Monoclonal/chemistry , Antibodies, Monoclonal/immunology , Antibody Specificity/immunology , Carcinoma/immunology , Genetic Variation , Protein Engineering/methods , Amino Acid Sequence , Animals , Antibodies, Monoclonal/biosynthesis , Antibodies, Monoclonal/genetics , Antibody Affinity , Antigens, Neoplasm/immunology , Base Sequence , Binding Sites, Antibody , Carcinoma/pathology , Cloning, Molecular , Genetic Variation/genetics , Germ-Line Mutation/genetics , Glycoproteins/immunology , Humans , Immunoglobulin Variable Region/biosynthesis , Immunoglobulin Variable Region/chemistry , Immunoglobulin Variable Region/genetics , Immunoglobulin Variable Region/immunology , Immunoglobulin kappa-Chains/biosynthesis , Immunoglobulin kappa-Chains/chemistry , Immunoglobulin kappa-Chains/genetics , Immunoglobulin kappa-Chains/immunology , Kinetics , Mice , Models, Molecular , Molecular Sequence Data , Peptide Library , Recombinant Fusion Proteins/biosynthesis , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/immunologyABSTRACT
An improved antibody modelling algorithm has been developed which incorporates significant improvements to the earlier versions developed by Martin et al. (1989, 1991), Pedersen et al. (1992) and Rees et al. (1996) and known as AbM (Oxford Molecular). The new algorithm, WAM (for Web Antibody Modelling), has been launched as an online modelling service and is located at URL http://antibody.bath.ac.uk. Here we provide a summary only of the important features of WAM. Readers interested in further details are directed to the website, which gives extensive background information on the methods employed. A brief description of the rationale behind some of the newer methodology (specifically, the knowledge-based screens) is also given.
