A Humanized Monoclonal Antibody Constructed from Intronless Expression Vectors Targets Human Hepatocellular Carcinoma Cells

An anti-human hepatocellular carcinoma (HCC) monoclonal antibody, hHP-1, was genetically humanized from a murine monoclonal antibody. In this study, a concept of positional template approach was applied to design the amino acid sequence of hHP-1's variable region, and synthetic DNA fragments for protein expression were produced through overlapping PCR from single strand oligonucleotides. Synthetic DNA fragments and human antibody constant region cDNA were used to construct two CMV promotor-based expression vectors for the antibody light and heavy chains, in which the variable region was connected directly to the constant region without an intron sequence. Completely assembled humanized antibody was successfully expressed in mammalian cells as IgG1 kappa molecules and purified using protein A affinity column. The immunogenicity of the hHP1 was estimated by the amino acid sequence and determined through a HAMA (human anti-murine antibody) serum reaction assay. Results indicated that the immunogenicity of hHP-1 was significantly reduced. In vitro binding activity assay showed that the hHP-1 had retained its binding function to a human HCC SMMC-7721 cell-line, without cross binding to other human normal tissues. Immunofluorescence staining showed that hHP-1 had a strong binding activity to SMMC cells. A competitive binding assay showed that the relative binding activity of hHP-1 was approximately 25% binding activity of the original murine antibody. Our results indicate that a humanized antibody could be produced using intronless vectors and expressed as a complete IgG1 kappa antibody. Hence we believe that hHP-1 could be a potential candidate for HCC treatment.