The naturally low secretory capacity of baker’s yeast presents an advantage over all other expression systems when it comes to mitigating the risk of host cell protein (HPC) immunogenicity. At Phenotypeca, we choose appropriately from our toolbox and key strain collection the best strains for initial expression and assays. Our combination of known rational engineering, a stable but exchangeable 2-micron expression vector, and breeding for optimising diversity and subsequent QTL analysis leading to IP has a proven record of improving titre, reducing undesired side products, improving fermentation and purification processes, leading to an overall cost of good for a premium product of high quality and commercially viable net yields. Even so, a vital step in ensuring the safety and efficacy of your final protein product is the effective removal of host cell proteins, which can be achieved by a combination of strain development and downstream processing techniques. In terms of strain development, the selected strains can be engineered to increase robustness to downstream processing to reduce cell lysis. Furthermore, settling can be increased to reduce centrifugation needs.
Our downstream processing team utilises a variety of purification techniques to determine the best protocol with the least loss of product for each protein project. As is the case in strain development, the removal of HCPs during downstream processing is primarily concerned with minimising lysis via the reduction of shear force stress. Concerning post-centrifugation/filtration techniques, an efficient approach is the use of chromatographic techniques capable of separating the protein of interest from host cell proteins based on factors such as charge (IEX), hydrophobicity (HIC) or size (SEC). Analytical techniques (e.g., mass spectrometry, ELISA, and HPLC) are used to inform and optimise downstream processing by identifying the levels of HCPs at each stage of purification.