Cellulose-based filter aids increase the capacity of depth filters during the downstream processing of plant-derived biopharmaceutical proteins.

Downstream processing (DSP) is a major cost factor during the production of biopharmaceutical proteins. Clarification can account for ∼40% of these costs, especially when a large amount of dispersed particulate material is generated, such as during the extraction of intracellular proteins from plants. Filter capacity can be increased (and DSP costs reduced) by using flocculants. Here we show that cellulose-based filter aids can enhance the positive effect of flocculants by improving depth filter capacity even further. A design-of-experiments (DoE) approach was used to identify the optimal size and concentration of filter aids, at different values of pH and conductivity, for the clarification of tobacco leaf extracts during the production of a monoclonal antibody and a fluorescent protein. Filter aids ∼28 or ∼100 μm in length at concentrations of ∼10 and ∼5 g L(-1) respectively were most efficient in combination with a strong cationic flocculant, but were ineffective without the flocculant. The filter aids increased depth filter capacity by 35-fold compared to an additive-free extract reaching ∼1000 L m(-2) without affecting the target proteins. Thus, filter aids can be used to reduce production costs of plant-derived biopharmaceuticals while the DoE approach enabled the identification of robust process conditions.