Cell banks are an essential component in the production of biopharmaceuticals, ensuring that the desired therapeutic proteins or biologics can be produced consistently, reliably, and in large quantities. The custom design of cell banks involves creating and maintaining a population of genetically engineered cells that can reliably express the target protein, often under optimized conditions. Below is an overview of the key aspects involved in designing and establishing custom cell banks for biopharmaceuticals.
Designing a custom cell bank requires consideration of several factors to ensure that the cells can efficiently produce the desired biopharmaceutical, and that the process remains robust over time. Below are key steps involved in the design process:
Selection of a Host Cell Line
The choice of host cell line is one of the first critical decisions in cell bank design. The host cell line determines the capacity for expression, post-translational modifications, and scalability of the final product. Common host cells include:
- Bacterial cells (e.g., E. coli): Often used for simpler proteins that do not require post-translational modifications.
- Yeast cells (e.g., Pichia pastoris): Used for proteins requiring some level of post-translational modifications and rapid growth.
Gene Expression System
- Selection of a Promoter: The expression system should include a strong promoter that drives the gene of interest's expression. The choice of promoter will depend on whether the system is inducible (for controlled expression) or constitutive.
- Incorporation of Selection Markers: Typically, antibiotic resistance genes (e.g., neomycin or hygromycin) are used to select for cells that have successfully incorporated the plasmid containing the gene of interest.
- Transfection/Transformation: The chosen host cell line will need to be transfected (for mammalian or insect cells) or transformed (for bacterial or yeast cells) with the plasmid containing the gene of interest. This step can be performed using chemical methods, electroporation, or viral vectors.
Cloning of High-Expression Cell Lines
- Cloning by Limiting Dilution or Single-Cell Sorting: After transfection, the cells are cultured and diluted to isolate individual clones. These clones are then screened for high expression levels of the target protein.
- Stabilization of Expression: Over time, cells can lose the ability to express the desired protein efficiently. To prevent this, the selected clones are subcloned, stabilized, and genetically modified to ensure long-term expression stability.
- Tailoring for Specific Products: The design of cell banks may be customized for specific biopharmaceuticals based on the nature of the product. For example, if the biopharmaceutical is an antibody, the cell line might be engineered to produce monoclonal antibodies in large quantities.
- High-Yield Clones: For large-scale production, the cell bank may focus on optimizing high-yield cell clones that express the therapeutic protein at the highest levels possible.
- Post-translational Modifications: For proteins requiring specific post-translational modifications (e.g., glycosylation patterns), the design of the cell bank may involve selecting or engineering host cells that can produce these modifications.