The case studied

The case studied was the purification of a recombinant protein produced by a Chinese hamster ovary cell line, provided by Swedish Orphan Biovitrum AB (Stockholm, Sweden). The purification process was based on the integrated downstream process presented in our previous study (Löfgren et al., 2018). In that study, the clarified supernatant was captured using a weak anion-exchange column (capture step), followed by a virus inactivation step and hydrophobic interaction chromatography (polishing step). In contrast to our previous study, we used a 3-column PCC operation as the capture step with prior continuous virus inactivation, as illustrated in Figure 1, and we implemented a real-time controller to adapt the system to changes in the load concentration.
Two of the three capture columns in the PCC operation are interconnected during the loading phase so that the product breakthrough from the first column is adsorbed on the second column, thus allowing the resin utilization to be increased without reducing the yield (Godawat et al., 2012; Gomis-Fons, Andersson, et al., 2020). At the same time, a third capture column carries out washing, elution, regeneration and equilibration phases (recovery phases). PCC runs periodically in three cycles consisting of two stages each: one in which the columns are interconnected during the loading phase, and the other in which they are interconnected during the washing phase (see Godawat et al., 2012 or Gomis-Fons, Andersson, et al., 2020 for further details). The position of the three capture columns is changed between each cycle.
Four different scenarios were compared to evaluate the performance of the implemented process: the process run in batch mode with the virus inactivation step followed by a single-column capture step and the polishing step (Case “Batch”), the integrated continuous process with constant load concentration (Case c0), and the integrated continuous process with a change in load concentration with and without control (Cases c1A and c1B, respectively). Case c1B was based on an extrapolation of Case c1A after the disturbance.