Introduction
Chinese Hamster Ovary (CHO) cells are widely used in the production of therapeutic monoclonal antibodies (mAbs) due to their ability to perform complex post-translational modifications, particularly glycosylation. CHO systems are essential in biopharmaceutical manufacturing, ensuring proper protein folding, functionality, and stability.

Mechanisms of Antibody Expression in CHO Cells
• Transfection of CHO Cells
The process begins with introducing plasmid DNA containing the genes for the heavy and light chains of the antibody into CHO cells. Transfection can be achieved through several methods, including electroporation or chemical reagents such as polyethyleneimine (PEI). High-efficiency transfection ensures sufficient gene expression and protein production. Both stable and transient transfection strategies can be used depending on the production needs.
• Transcription and Translation
The plasmid DNA integrates into the CHO genome or remains episomal, where it is transcribed by the host's machinery. Strong promoters, such as the CMV promoter, drive transcription, enhancing RNA production. After transcription, ribosomes translate the mRNA into antibody polypeptides in the cytoplasm.
• Protein Folding and Assembly in the Endoplasmic Reticulum (ER)
The heavy and light chains of the antibody enter the ER, where they undergo folding, assisted by chaperone proteins like BiP and PDI. Disulfide bond formation ensures the correct conformation of the antibody. Misfolded proteins are tagged for degradation via the ER-associated degradation (ERAD) pathway.
• Post-Translational Modifications
CHO cells perform essential modifications, including N-linked glycosylation, within the ER and Golgi apparatus. This glycosylation ensures structural stability and influences biological activities such as antibody-dependent cellular cytotoxicity (ADCC).
• Secretion into the Extracellular Space
After proper folding and glycosylation, the assembled antibodies are transported to the Golgi and then secreted into the culture medium. Efficient secretion ensures high yields for downstream purification.
• Fed-Batch Culture Optimization
To maximize antibody yields, CHO cells are cultured in fed-batch systems, where nutrients such as glucose, amino acids, and vitamins are replenished throughout the process. This strategy maintains cell viability and productivity over extended periods.
• Gene Amplification for Yield Improvement
Gene amplification systems like dihydrofolate reductase (DHFR) are employed to increase the copy number of the antibody-encoding genes, enhancing production. CHO-DG44 cells, which lack DHFR activity, are often used to allow selective pressure for gene amplification.

Applications in Therapeutics
CHO cell-derived antibodies are essential in many therapeutic applications due to their similarity to human antibodies in terms of structure and glycosylation patterns. They are employed in treatments for:
• Cancer therapy: e.g., Trastuzumab and Rituximab.
• Autoimmune diseases: e.g., Adalimumab for rheumatoid arthritis.
• Infectious diseases: e.g., monoclonal antibodies targeting SARS-CoV-2.
The ability of CHO cells to generate complex glycoforms allows the production of antibodies with enhanced half-life or altered effector functions, such as antibody-dependent cellular cytotoxicity (ADCC) or complement-dependent cytotoxicity (CDC).

Tools and Services from GenScript
GenScript offers tools and services for CHO-based antibody production, such as:
• GenScript TurboCHO™ SmartQuote Tool offers instant quotes and easy order processing.
• TurboCHO™ Express Platform can deliver a range of purified antibody products.
• TurboCHO™ Stable Cell Pool & Cell Line Platform provides high expression levels for high-quality recombinant proteins/antibodies with fast turnaround times.
• TurboCHO™ Antibody Expression Platform provides a cost-effective and time-efficient solution for various stages of antibody research.

Conclusion
CHO cell expression systems are at the forefront of therapeutic antibody production, offering scalability and the ability to perform essential post-translational modifications. Advances in bioprocess engineering and cell line development continue to optimize antibody yields and quality, ensuring their pivotal role in modern therapeutics. The flexibility of CHO systems in meeting clinical-grade production standards highlights their enduring relevance in pharmaceutical manufacturing.