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Abstract The Chinese hamster ovary (CHO) cell lines that are used to produce commercial quantities of therapeutic proteins commonly exhibit a decrease in productivity over time in culture, a phenomenon termed production instability. Random integration of the transgenes encoding the protein of interest into locations in the CHO genome that are vulnerable to genetic and epigenetic instability often causes production instability through copy number loss and silencing of expression. Several recent publications have shown that these cell line development challenges can be overcome by using site‐specific integration (SSI) technology to insert the transgenes at genomic loci, often called “hotspots,” that are transcriptionally permissive and have enhanced stability relative to the rest of the genome. However, extensive characterization of the CHO epigenome is needed to identify hotspots that maintain their desirable epigenetic properties in an industrial bioprocess environment and maximize transcription from a single integrated transgene copy. To this end, the epigenomes and transcriptomes of two distantly related cell lines, an industrially relevant monoclonal antibody‐producing cell line and its parental CHO‐K1 host, were characterized using high throughput chromosome conformation capture and RNAseq to analyze changes in the epigenome that occur during cell line development and associated changes in system‐wide gene expression. In total, 10.9% of the CHO genome contained transcriptionally permissive three‐dimensional chromatin structures with enhanced genetic and epigenetic stability relative to the rest of the genome. These safe harbor regions also showed good agreement with published CHO epigenome data, demonstrating that this method was suitable for finding genomic regions with epigenetic markers of active and stable gene expression. These regions significantly reduce the genomic search space when looking for CHO hotspots with widespread applicability and can guide future studies with the goal of maximizing the potential of SSI technology in industrial production CHO cell lines.
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A Flexible Hybrid Site‐Specific Integration‐Based Expression System in CHO Cells for Higher‐Throughput Evaluation of Monoclonal Antibody Expression Cassettes
ABSTRACT The implementation of site‐specific integration (SSI) systems in Chinese hamster ovary (CHO) cells for the production of monoclonal antibodies (mAbs) can alleviate concerns associated with production instability and reduce cell line development timelines. SSI cell line performance is driven by the interaction between genomic integration location, clonal background, and the transgene expression cassette, requiring optimization of all three parameters to maximize productivity. Systematic comparison of these parameters has been hindered by SSI platforms involving low‐throughput enrichment strategies, such as cell sorting. This study presents a recombinase‐mediated cassette exchange (RMCE)‐capable SSI system that uses only chemical selection to enrich for transgene‐expressing RMCE pools in less than one month. The system was used to compare eight mAb expression cassettes containing two novel genetic regulatory elements, theAzin1CpG island and the Piggybac transposase 5’ terminal repeat, in various orientations to improve the expression of two therapeutic mAbs from two genomic loci. Similar patterns of productivity and mRNA expression were observed across sites and mAbs, and the best performing cassette universally increased mAb productivity by 7‐ to 11‐fold. This flexible system allows for higher‐throughput comparison of expression cassettes from a consistent clonal and transcriptional background to optimize RMCE‐derived cell lines for industrial production of mAbs.
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- Award ID(s):
- 2100502
- PAR ID:
- 10570553
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Biotechnology Journal
- Volume:
- 20
- Issue:
- 1
- ISSN:
- 1860-6768
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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