Efficient CRISPR/Cas9-Mediated BAX Gene Ablation in CHO Cells To Impair Apoptosis and Enhance Recombinant Protein Production

From Efficiency to Yield: Exploring Recent Advances in CHO Cell Line Development for Monoclonal Antibodies

The increasing demand for biosimilar monoclonal antibodies (mAbs) has prompted the development of stable high-producing cell lines while simultaneously decreasing the time required for screening. Existing platforms have proven inefficient, resulting in inconsistencies in yields, growth characteristics, and quality features in the final mAb products. Selecting a suitable expression host, designing an effective gene expression system, developing a streamlined cell line generation approach, optimizing culture conditions, and defining scaling-up and purification strategies are all critical steps in the production of recombinant proteins, particularly monoclonal antibodies, in mammalian cells. As a result, an active area of study is dedicated to expression and optimizing recombinant protein production. This review explores recent breakthroughs and approaches targeted at accelerating cell line development to attain efficiency and consistency in the synthesis of therapeutic proteins, specifically monoclonal antibodies. The primary goal is to bridge the gap between rising demand and consistent, high-quality mAb production, thereby benefiting the healthcare and pharmaceutical industries.

Recombinant therapeutic proteins degradation and overcoming strategies in CHO cells

Mammalian cell lines are frequently used as the preferred host cells for producing recombinant therapeutic proteins (RTPs) having post-translational modified modification similar to those observed in proteins produced by human cells. Nowadays, most RTPs approved for marketing are produced in Chinese hamster ovary (CHO) cells. Recombinant therapeutic antibodies are among the most important and promising RTPs for biomedical applications. One of the issues that occurs during development of RTPs is their degradation, which caused by a variety of factors and reducing quality of RTPs. RTP degradation is especially concerning as they could result in reduced biological functions (antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity) and generate potentially immunogenic species. Therefore, the mechanisms underlying RTP degradation and strategies for avoiding degradation have regained an interest from academia and industry. In this review, we outline recent progress in this field, with a focus on factors that cause degradation during RTP production and the development of strategies for overcoming RTP degradation. KEY POINTS: • The recombinant therapeutic protein degradation in CHO cell systems is reviewed. • Enzymatic factors and non-enzymatic methods influence recombinant therapeutic protein degradation. • Reducing the degradation can improve the quality of recombinant therapeutic proteins.

Time and Cost-Effective Genome Editing Protocol for Simultaneous Caspase 8 Associated Protein 2 Gene Knock in/out in Chinese Hamster Ovary Cells Using CRISPR-Cas9 System

Background

CHO cells are preferred for producing biopharmaceuticals, and genome editing technologies offer opportunities to enhance recombinant protein production. Targeting apoptosis-related genes, such as Caspases 8-Associated Protein 2 (CASP8AP2), improves CHO cell viability and productivity. Integrating robust strategies with the CRISPR-Cas9 system enables its application in CHO cell engineering.

Objectives

This study was performed to develop a cost-effective protocol using the CRISPR-Cas9 system combined with the HITI strategy for simultaneous CASP8AP2 gene deletion/insertion in CHO cells and to assess its impact on cell viability and protein expression.

Materials and Methods

We developed an efficient protocol for CHO cell engineering by combining CRISPR/Cas9 with the HITI strategy. Two distinct sgRNA sequences were designed to target the 3' UTR region of the CASP8AP2 gene using CHOPCHOP software. The gRNAs were cloned into PX459 and PX460-1 vectors and transfected into CHO cells using the cost-effective PEI reagent. A manual selection system was employed to streamline the process of single-cell cloning. MTT assays assessed gene silencing and cell viability at 24, 48, and 72 hours. Flow cytometry evaluated protein expression in CASP8AP2-silenced CHO cells.

Results

The study confirmed the robustness of combining CRISPR-Cas9 with the HITI strategy, achieving a high 60% efficiency in generating knockout clones. PEI transfection successfully delivered the constructs to nearly 65% of the clones, with the majority being homozygous. The protocol proved feasible for resource-limited labs, requiring only an inverted fluorescent microscope. CASP8AP2 knockout (CHO-KO) cells exhibited significantly extended cell viability compared to CHO-K1 cells when treated with NaBu, with IC50 values of 7.28 mM and 14.25 mM at 48 hours, respectively (P-value 24 hours ≤ 0.0001, 48 hours ≤ 0.0001, P-value 72 hours = 0.0007). CHO CASP8AP2-silenced cells showed a 1.3-fold increase in JRed expression compared to native cells.

Conclusions

CRISPR-Cas9 and HITI strategy was used to efficiently engineer CHO cells for simultaneous CASP8AP2 gene deletion/insertion, which improved cell viability and protein expression.