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.