Proteins with therapeutic applications are synthesised in the laboratory for pharmaceutical use. Many recombinant DNA-based processes use genetically modified micro-organisms as host cells (bacteria, yeast or mammalian cells) to produce biological products, under defined conditions, that they would not normally create in their natural form. Insulin was the first therapeutic protein to be introduced to treat diabetes in the 1920s.
Depending on the requirements of the protein, the choice of host cell is critical. Mammalian cells are most often selected because their post-translational modifications, such as glycosylation and sialylation, have the biggest impact on the protein’s pharmacokinetics and efficiency.
The cells are cultured by fermentation. The modified DNA chain, with the altered gene and the substances that it codes for, develop simultaneously. The desired cell products may be produced intra- or extracellularly.
After fermentation, the micro-organisms are extracted by continuously operating separators. To increase the yield, the solid material is washed and extracted by centrifugation. The clarified phases of the two stages are mixed and fed to further stages of the process. All material streams leaving this enclosed process must be sterilized at temperatures of at least 121 °C. To keep the process as simple as possible, the biomass is harvested directly after fermentation, in the fermenter, by heat or by chemical methods. Completely enclosed, steam-sterilized centrifuges are employed in this process and can be connected to other equipment in a sterile manner.
Intracellular Products and Inclusion Bodies
In intracellular processes, it is differentiated whether the desired product is contained in the intracellular liquid or in so-called inclusion bodies. In contrast to extracellular bioproduction, the clarified phase leaves the process here and the biomass is processed.
The washed and concentrated biomass is homogenized; that is, the cells are broken down and the intracellular liquid and the inclusion bodies are released. These are separated from the cell fragments, washed and concentrated in further stages of the process by centrifuges. For intracellular products gained from the cell liquid, the solids are extracted by continuously operating separators.