An IRES-Mediated Tricistronic Vector for Efficient Generation of Stable, High-Level Monoclonal Antibody Producing CHO DG44 Cell Lines

The generation of stable, high-level monoclonal antibody (mAb) producing cell lines remains a major challenge in biopharmaceutical industry. The commonly used plasmid vectors for mAb expression, which express light chain (LC), heavy chain (HC), and selection marker genes on separate vectors or via multiple promoters on a single vector, are not able to accurately control the ratio of LC over HC expression and tend to result in non-expressing clones. To overcome these issues, we have developed a tricistronic vector using two internal ribosome entry sites (IRES) to express the LC, HC, and dihydrofolate reductase (DHFR) selection marker genes in one transcript. In this tricistronic vector, the three genes are under the control of a hapten-modified human cytomegalovirus (hCMV) promoter containing a core CpG island element (IE) to enhance the production stability. The LC gene is arranged as the first cistron followed by a wild-type IRES to control the HC expression. Such design expresses excess LC polypeptides which enhance mAb expression level and reduce aggregate. A mutated IRES with attenuated strength is applied on DHFR to reduce its expression for enhancing the stringency of selection for high producers. This vector allows easy generation of stable, high mAb producing CHO DG44 pools and clones for antibody development and manufacturing.