Bax and Bak knockout apoptosis-resistant CHO cell lines significantly improve culture viability and titer in intensified fed-batch culture process

A systemic approach to identifying sequence frameworks that decrease mAb production in a transient Chinese hamster ovary cell expression system

Monoclonal antibodies (mAbs) are often engineered at the sequence level for improved clinical performance yet are rarely evaluated prior to candidate selection for their "developability" characteristics, namely expression, which can necessitate additional resource investments to improve the manufacturing processes for problematic mAbs. A strong relationship between primary sequence and expression has emerged, with slight differences in amino acid sequence resulting in titers differing by up to an order of magnitude. Previous work on these "difficult-to-express" (DTE) mAbs has shown that these phenotypes are driven by post-translational bottlenecks in antibody folding, assembly, and secretion processes. However, it has been difficult to translate these findings across cell lines and products. This work presents a systematic approach to study the impact of sequence variation on mAb expression at a larger scale and under more industrially relevant conditions. The analysis found 91 mutations that decreased transient expression of an IgG1κ in Chinese hamster ovary (CHO) cells and revealed that mutations at inaccessible residues, especially those leading to decreases in residue hydrophobicity, are not favorable for high expression. This workflow can be used to better understand sequence determinants of mAb expression to improve candidate selection procedures and reduce process development timelines.

Engineering mammalian cell growth dynamics for biomanufacturing

Precise control over mammalian cell growth dynamics poses a major challenge in biopharmaceutical manufacturing. Here, we present a multi-level cell engineering strategy for the tunable regulation of growth phases in mammalian cells. Initially, we engineered mammalian death phase by employing CRISPR/Cas9 to knockout pro-apoptotic proteins Bax and Bak, resulting in a substantial attenuation of apoptosis by improving cell viability and extending culture lifespan. The second phase introduced a growth acceleration system, akin to a "gas pedal", based on an abscidic acid inducible system regulating cMYC gene expression, enabling rapid cell density increase and cell cycle control. The third phase focused on a stationary phase inducing system, comparable to a "brake pedal". A tetracycline inducible genetic circuit based on BLIMP1 gene led to cell growth cessation and arrested cell cycle upon activation. Finally, we developed a dual controllable system, combining the "gas and brake pedals", enabling for dynamic and precise orchestration of mammalian cell growth dynamics. This work exemplifies the application of synthetic biology tools and combinatorial cell engineering, offering a sophisticated framework for manipulating mammalian cell growth and providing a unique paradigm for reprogramming cell behaviour for enhancing biopharmaceutical manufacturing and further biomedical applications.

Activation of the PERK branch of the unfolded protein response during production reduces specific productivity in CHO cells via downregulation of PDGFRa and IRE1a signaling

During the course of biopharmaceutical production, heterologous protein expression in Chinese hamster ovary (CHO) cells imposes a high proteostatic burden that requires cellular adaptation. To mitigate such burden, cells utilize the unfolded protein response (UPR), which increases endoplasmic reticulum (ER) capacity to accommodate elevated rates of protein synthesis and folding. In this study, we show that during production the UPR regulates growth factor signaling to modulate growth and protein synthesis. Specifically, the protein kinase R-like ER kinase (PERK) branch of the UPR is responsible for transcriptional down-regulation of platelet-derived growth factor receptor alpha (PDGFRa) and attenuation of the IRE1-alpha (IRE1a) branch of the UPR. PERK knockout (KO) cell lines displayed reduced growth and viability due to higher rates of apoptosis despite having stabilized PDGFRa levels. Knocking out PERK in an apoptosis impaired (Bax/Bak double KO) antibody-expressing cell line prevented apoptotic cell death and revealed that apoptosis was likely triggered by increased ER stress and reactive oxygen species levels in the PERK KO hosts. Our findings suggest that attenuation of IRE1a and PDGFRa signaling by the PERK branch of the UPR reduces ER protein folding capacity and hence specific productivity of CHO cells in order to mitigate UPR and prevent apoptotic cell death. Last, Bax/Bak/PERK triple KO CHO cell lines displayed 2-3 folds higher specific productivity and titer (up to 8 g/L), suggesting that modulation of PERK signaling during production processes can greatly improve specific productivity in CHO cells.

Overexpression of SIRT6 alleviates apoptosis and enhances cell viability and monoclonal antibody expression in CHO-K1 cells

BACKGROUND

Chinese hamster ovary (CHO) cells are the most predominantly utilized host for the production of monoclonal antibodies (mAbs) and other complex glycoproteins. A major challenge in the process of CHO cell culture is the occurrence of cell death following different stressful conditions, which hinders the production yield. Engineering genes involved in pathways related to cell death is a remarkable strategy to delay apoptosis, improve cell viability and enhance productivity. SIRT6 is a stress-responsive protein that regulates DNA repair, maintains genome integrity, and is critical for longevity and cell survival in organisms.

METHODS AND RESULTS

In this study, SIRT6 was stably overexpressed in CHO-K1 cells and the impact of its expression on apoptosis related gene expression profile, viability, apoptosis, and mAb productivity was investigated. While a significant increase was observed in Bcl-2 mRNA level, caspase-3 and Bax mRNA levels were decreased in the SIRT6 engineered cells compared to the parental CHO-K1 cells. Moreover, improved cell viability and decreased rate of apoptotic progression was observed in a SIRT6-derived clone in comparision to the CHO-K1 cells during 5 days of batch culture. anti-CD52 IgG1 mAb titers were improved up to 1.7- and 2.8-fold in SIRT6-derived clone during transient and stable expression, respectively.

CONCLUSIONS

This study indicates the positive effects of SIRT6 overexpression on cell viability and anti-CD52 IgG1 mAb expression in CHO-K1 cells. Further studies are needed to examine the potential of SIRT6-engineered host cells for the production of recombinant biotherapeutics in industrial settings.

CRISPR Technologies in Chinese Hamster Ovary Cell Line Engineering

The Chinese hamster ovary (CHO) cell line is a well-established platform for the production of biopharmaceuticals due to its ability to express complex therapeutic proteins with human-like glycopatterns in high amounts. The advent of CRISPR technology has opened up new avenues for the engineering of CHO cell lines for improved protein production and enhanced product quality. This review summarizes recent advances in the application of CRISPR technology for CHO cell line engineering with a particular focus on glycosylation modulation, productivity enhancement, tackling adventitious agents, elimination of problematic host cell proteins, development of antibiotic-free selection systems, site-specific transgene integration, and CRISPR-mediated gene activation and repression. The review highlights the potential of CRISPR technology in CHO cell line genome editing and epigenetic engineering for the more efficient and cost-effective development of biopharmaceuticals while ensuring the safety and quality of the final product.

CRISPR-interceded CHO cell line development approaches

For industrial production of recombinant protein biopharmaceuticals, Chinese hamster ovary (CHO) cells represent the most widely adopted host cell system, owing to their capacity to produce high-quality biologics with human-like posttranslational modifications. As opposed to random integration, targeted genome editing in genomic safe harbor sites has offered CHO cell line engineering a new perspective, ensuring production consistency in long-term culture and high biotherapeutic expression levels. Corresponding the remarkable advancements in knowledge of CRISPR-Cas systems, the use of CRISPR-Cas technology along with the donor design strategies has been pushed into increasing novel scenarios in cell line engineering, allowing scientists to modify mammalian genomes such as CHO cell line quickly, readily, and efficiently. Depending on the strategies and production requirements, the gene of interest can also be incorporated at single or multiple loci. This review will give a gist of all the most fundamental recent advancements in CHO cell line development, such as different cell line engineering approaches along with donor design strategies for targeted integration of the desired construct into genomic hot spots, which could ultimately lead to the fast-track product development process with consistent, improved product yield and quality.