Single-chain antibody construction and functional mapping of the monoclonal antibody TS1 : Its interaction with the antigen and the anti-idiotype

Abstract: The aims of this study are to synthesize and produce a single-chain antibody (scFv) of the anti-cytokeratin 8 monoclonal IgG antibody TS1 and to functionally map amino acid residues important for the interaction with its antigen and the anti-idiotypic antibody TS1. The TS1 antibody has been shown to be effective in binding cytokeratin 8 (CK8) expressed in tumors in vivo and is proposed to be useful in immunotargeting and/or immunotherapy. The anti-idiotypic antibody TS1 can be used to regulate the tumor:non-tumor ratio. Mutagenesis of certain amino acid residues can be used to alter the affinity to improve the tumor:non-tumor ratio further. In the present study, the TS1 IgG was chemically modified to specify groups of residues important for interaction with both CK8 and TS1. If important residues were found in the CDRs, they were mutated in the TS1 scFv construct and the effect was studied using ELISA. The main conclusions drawn from this study are that the important amino acid residues in TS1 for the interaction with both CK8 and TS1 are mainly tyrosines, charged residues and a tryptophan. A central interacting interface was identified with the somewhat unusual participation of residues in the CDR 2 of the light chain. Mutations which resulted in increased affinity to both CK8 and TS1 were also identified.