Class-switching of the IgM type antiadenocarcinoma human antibody HB4C5 into an IgG1 type resulted in the loss of the antigen binding ability

Abstract

The heavy and light chain genes (mu and lambda) of the human anti-adenocarcinoma monoclonal antibody HB4C5 (MAb-C5) were cloned from the human-human hybridoma cell line HB4C5 and co-expressed in Chinese hamster ovary (CHO) and COS-7 cells. ELISA assay and the RI imaging of the cancer tissue xenografted into nude mice showed that the recombinant MAb-C5 retained the original antigen binding activity. We then replaced the IgM constant region of the MAb-C5 heavy chain gene with the human IgG1 constant region gene and co-expressed it with the light chain gene. This recombination was confirmed by a complete DNA sequencing and Western-blot analysis. Despite the fact that the DNA sequence, the expressed protein size, and the assembly of heavy and light chains were indicated to be normal, the IgG1 type MAb-C5 could not bind to the original antigen. This result suggest that this antibody alters its antigen binding property upon class-switching.