Single Copy Transgene Integration in a Transcriptionally Active Site for Recombinant Protein Synthesis

For the biomanufacturing of protein biologics, establishing stable cell lines with high transgene transcription is critical for high productivity. Modern genome engineering tools can direct transgene insertion to a specified genomic locus and can potentially become a valuable tool for cell line generation. In this study, the authors survey transgene integration sites and their transcriptional activity to identify characteristics of desirable regions. A lentivirus containing destabilized Green Fluorescent Protein (dGFP) is used to infect Chinese hamster ovary cells at a low multiplicity of infection, and cells with high or low GFP fluorescence are isolated. RNA sequencing and Assay for Transposase Accessible Chromatin using sequencing data shows integration sites with high GFP expression are in larger regions of high transcriptional activity and accessibility, but not necessarily within highly transcribed genes. This method is used to obtain high Immunoglobulin G (IgG) expressing cell lines with a single copy of the transgene integrated into transcriptionally active and accessible genomic regions. Dual recombinase‐mediated cassette exchange is then employed to swap the IgG transgene for erythropoietin or tumor necrosis factor receptor‐Fc. This work thus highlights a strategy to identify desirable sites for transgene integration and to streamline the development of new product producing cell lines. For the biomanufacturing of protein biologics, establishing stable cell lines with high transgene transcription is critical for high productivity. In this study, the authors obtain CHO cell lines with a single integration site of a transgene into a transcriptionally active and open region of the genome, and show that the single copy cell line can be used for transgene exchange. This work highlights a strategy to identify desirable sites for transgene integration and to streamline the development of new product producing cell lines.