Approaches to Controlled Co-Amplification of Genes for Production of Biopharmaceuticals: Study of the Insertion and Amplification Dynamics of Genetic Cassettes in the Genome of Chinese Hamster Ovary Cells during Co-Expression of Compatible Pair of Plasmids.

Plasmid vector family p1.1 based on non-coding regions of Chinese hamster housekeeping gene EEF1A and concatemer of Epstein-Barr virus terminal repeat increases the frequency of genome integration and provides rapid amplification of the target genes in the genome. For a pair of fluorescent proteins eGFP and mCherry it was shown that p1.1 vectors bearing dihydrofolate reductase and glutamine synthetase selection markers upon co-transfection into CHO DG44 cell line allow obtaining a polyclonal cell population in which ~70% of cells express both genes. The subsequent one-step gene amplification of the genome-integrated genetic cassettes under the selective pressure of increased concentrations of methotrexate can increase the expression of both integrated genes up to 8.2% eGFP and 9.9% mCherry of total protein. This approach can be used for the development of cell lines for the production of functional heterodimeric proteins, e.g. polypeptide hormones and therapeutic antibodies.