Expression System

Expression System designates the biological host and associated genetic elements used to produce recombinant proteins, nucleic acids, or viral vectors through controlled gene expression. Common expression systems include bacterial hosts like Escherichia coli, yeast, insect cells, and mammalian cell lines such as CHO, each offering distinct advantages regarding yield, folding capability, and post-translational modifications.

The biopharmaceutical industry selects expression systems based on therapeutic modality requirements, as complex biologics often require mammalian systems for correct glycosylation and folding, while simpler proteins may be produced efficiently in microbial hosts. Development includes vector design, promoter selection, clone screening, and optimisation of culture conditions. Regulatory submissions include extensive expression system characterisation addressing genetic stability, adventitious agent risk, and manufacturing consistency. Changes to expression systems represent major development decisions requiring significant comparability assessments. As new modalities emerge and manufacturing pressures intensify, expression system innovation continues through engineered cell lines and synthetic biology tools.