Characterization of human anti-EpCAM antibodies for developing an antibody-drug conjugate.

We previously generated fully human antibody-producing TC-mAb mice for obtaining potential therapeutic monoclonal antibodies (mAbs). In this study, we investigated 377 clones of fully human mAbs against a tumor antigen, epithelial cell adhesion molecule (EpCAM), to determine their antigen binding properties. We revealed that a wide variety of mAbs against EpCAM can be obtained from TC-mAb mice by the combination of epitope mapping analysis of mAbs to EpCAM and native conformational recognition analysis. Analysis of 72 mAbs reacting with the native form of EpCAM indicated that the EpCL region (amino acids 24-80) is more antigenic than the EpRE region (81-265), consistent with numerous previous studies. To evaluate the potential of mAbs against antibody-drug conjugates, mAbs were directly labeled with DM1, a maytansine derivative, using an affinity peptide-based chemical conjugation (CCAP) method. The cytotoxicity of the conjugates against a human colon cancer cell line could be clearly detected with high-affinity as well as low-affinity mAbs by the CCAP method, suggesting the advantage of this method. Thus, this study demonstrated that TC-mAb mice can provide a wide variety of antibodies and revealed an effective way of identifying candidates for fully human ADC therapeutics.