For decades, research groups around the world have devoted enormous efforts to improving the performance of productive CHO cell lines. Attempts at these cell line manipulations are aimed at achieving higher productivity and product yield, and leverage existing knowledge on transcription, translation, cellular metabolism, signaling pathways, and secretion mechanisms. The main strategies for host cell engineering are based on the overexpression of genes favoring cell proliferation, longevity, stress resistance and apoptosis, protein production and secretion. Numerous studies have shown that transient or stable overexpression of key genes involved in cell metabolism, protein biosynthesis, and glycosylation increases growth rate and productivity, respectively, and improves product quality.
Many biopharmaceutical companies follow a policy of developing their own production cell lines, but this practice has changed over the past decade. Companies now tend to use the same host cell line for production and initial clinical trials, as they have realized that this strategy simplifies the cycle of cell line development and optimizes the path to the clinic. Additionally, it reduces the risk of product comparability issues, helping manufacturers meet product quality requirements and consistency expectations.
These changing priorities have led to new directions for innovation in the CHO expression platform. The focus of industrial cell line development has shifted to the issue of host cell line stability to ensure stable long-term production, expression optimization using targeted integration technologies, especially complex engineered recombinant therapeutics, and the development of selection and screening systems for faster and more efficient Efficient clonal selection.
All CHO cells used in the pharmaceutical industry are characterized by good adaptability to genetic manipulation and changing culture conditions. This feature is a consequence of the inherently plastic genome of these cell lines, which makes them suitable for large-scale industrial production. On the downside, this cellular plasticity makes CHO cells more prone to genome rearrangements (deletions, translocations) and is a source of cell line instability during bioproduction. Production cells are under high genomic and metabolic demands, which can lead to genomic and epigenetic changes, resulting in decreased productivity and product quality.
Nonetheless, the numerous advantages offered by CHO cell lines make them ideal hosts for recombinant protein production, and therefore, it is unlikely that science and industry will abandon this expression system in the near future. Consequently, much effort has recently been devoted to understanding the phenomenon of instability in CHO cell lines. Research is focused on finding solutions to overcome phenotypic instability during manufacturing to ensure long-term stable production, process consistency and ensure acceptable product quality.
An important issue during the development of stable recombinant cell lines is the generation and identification of high-producing clones that do not lose their expressive capacity over time. (Clonality is considered critical in therapeutic protein production, as clonal lineages are thought to provide a stable and consistent product quality profile.) The production of selected clones then needs to be assessed during long-term culture, a labor-intensive process. tedious and time-consuming process. However, the rapidly accumulating transcriptome data on CHO cell lines has opened the way for functional analyzes to identify regulators and biomarkers of high yield and clonal stability.
Systems biology approaches open a new dimension for enhanced CHO-based bioproduction. Omics technologies offer new opportunities to better characterize and understand complex cellular functions, thereby laying the foundation for the possibility of mechanism-driven optimization of cell lines rather than manipulating a few key genes. However, a major problem is that these modern techniques require special instruments, materials, advanced information technology facilities, so they are still too complicated and expensive to be routinely used in industrial manufacturing. On the other hand, so far, the data provided by different omics techniques cannot be integrated into a common mathematical model, which will facilitate the transfer and application of this information in the design of experimental procedures.