Nutritional and cell culture process requirements vary between cell type, recombinant protein type and even between transfected clones. To maximise productivity of the biologically active protein, the cell culture process and relevant media must be optimised for each selected clone. This is further complicated by the large number of variables and by the fact that each transfectant may have different nutritional requirements for growth phase and production phase. Process and media optimisation has a major downstream impact on titre, manufacturability, costs and hence long-term profits; however, it is a significant challenge to optimise these factors under time pressure and in a cost-efficient manner.
Mammalian cell culture media for biotechnology are complex, chemically defined mixtures of carbohydrates, amino acids, lipids, growth factors, vitamins, minerals and undefined or partially defined hydrolysates. Use of serum-free media reduces batch-to-batch variation and avoids the compliance issues associated with animal-derived components. It also increases the extent to which optimisation is possible because all components of the media are fully defined.
Media optimisation strategies may involve titrating different nutrients into the medium to find the best combination (the 'top-down' approach) or analysing spent medium to investigate nutrient depletion and by-product accumulation (the 'bottom-up' approach). In addition it is vital to maintain the quality and correct biological activity of the secreted therapeutic protein.
Process optimisation concerns parameter settings such as cell seeding density and temperature shift, as well as feeding strategies, scaling up, validation and regulatory compliance. Most production systems use a fed-batch culture strategy where a basal medium (as used in clone selection) promotes early growth and production, and a feed medium provides the nutrients to support higher cell densities and maximum productivity.
To accelerate timelines, initial optimisation studies are best carried out early, while the top candidate clones are still being characterised. Cell line development groups can use the Cell Metric CLD™ for media optimisation in a small-scale format, such as in 24- or 6-well microplates. This strategy gives the operator a head start and reduces the overall costs and time required.
Advantages of using the Cell Metric CLD™ for initial optimisation include:
The next step
A small number of clones are now taken forward for scale-up testing.
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