Isolation and Evaluation of Specific Human Recombinant Antibodies from a Phage Display Library against HER۳ Cancer Signaling Antigen

Background: The human epidermal growth factor receptor family comprises four homologous members: EGFR (ErbB۱), ErbB۲ (HER۲), ErbB۳ (HER۳) and ErbB۴ (HER۴).This family plays an important role in the signaling pathway and cell proliferation. The heterodimerization of HER۲ with HER۳ leads to tumor cell proliferation. Monoclonal antibody to the human HER۳ receptor blocks HER۳ het- erodimerization and inhibits the growth of breast cancer cells. Due to their human origin, small size, rapid penetration and high affinity properties, recombinant single chain antibodies (scFv) have been introduced as the most desired agents for cancer immunotherapy. In this study, we use a phage display system to select specific scFvs against HER۳ for their use in cancer targeted therapy.Methods: A phage antibody display library of scFv was panned against an immunodominant epitope of HER۳. Phage rescue was performed on the library. The supernatant that contained the appropriate scFv (۱۰۹ PFU/ml) was added to an immunotube which was coated with the peptide. Elution was done using log phase E. coli TG۱. The clones were amplified by PCR and DNA fingerprinted to select the specific clones against the epitope. The specificity of the selected antibodies was tested in ELISA.Results: The results represented two predominant patterns with the frequency of ۲۵%. The other patterns showed the frequencies of ۵%-۱۰%. scFv۱ and scFv۲ demonstrated positive ELISA with absorbances of ۰.۶۳ and ۰.۴۶, respectively while the absorbances of wells without peptide were ۰.۱۹ and ۰.۱۱, respectively.Conclusion: In this study two specific scFvs were selected against HER۳ antigen in a successful panning process. Phage ELISA represented the specific binding of scFvs against HER۳.The selected scFvs reacted only with the corresponding peptides. However, no reaction with the other peptides was detected. The selected anti-HER۳ scFvs have suggested that these human high affinity and small antibodies that bind specifically to HER۳ epitope can be considered in HER۳ targeted approaches.