An overview of downstream processing in biologics

The term biologics refers to a broader spectrum of medicinal products comprising vaccines, plasma-derived proteins, enzymes, hormones, peptides, and larger molecules such as monoclonal antibodies. The current trend in biologics also includes cell and gene therapy molecules. The goal of this chapter is to highlight the purification techniques used to produce therapeutic proteins expressed in mammalian cell cultures. Upstream processing, downstream processing, and formulation make up the production process of proteins expressed in living hosts such as microbial, mammalian, insect, or plant cells. The upstream procedure often entails clone selection along with a variety of operations, from vial thawing to harvesting. The downstream processing development involves establishing a purification process train to capture the product from the cell culture harvest and further remove the product and process-related impurities along with the removal of viral contaminants to achieve a product with desirable purity and concentration. Formulation activities involve the preparation of the formulated drug substance by the addition of suitable buffers, excipients, and stabilizers to enhance the shelf-life of the protein without compromising on the purity and quality. The primary objective of any purification process is to achieve desirable purity with maximum yield by a robust, reliable, and scalable process. The general unit operations that are employed in the purification process include centrifugation, precipitation, flocculation, filtration, chromatography, crystallization, enzymatic reactions, nanofiltration, tangential flow filtration, and lyophilization. Each step of the purification process is designed to capture, polish, or remove a specific impurity and modulate the product to enhance its physiochemical and biological activity.