Conclusions
An integrated continuous downstream process with PCC and continuous
virus inactivation with detergent was successfully implemented in a
two-system setup in a case study of the purification of a recombinant
protein on laboratory scale. The 3-column PCC operation was designed
with minimal experimental effort as only a breakthrough curve was
necessary to obtain the required flow rates and cycles times. The
residence time distribution in the continuous virus inactivation step
was obtained experimentally to check that the protein had a minimum
residence time of 60 min. A simple yet effective real-time loading
controller based on iterative learning control was implemented to allow
adaptation of the downstream process to a change in the load
concentration. After a 20% decrease in concentration, the cycle length
was automatically adjusted, giving almost the same product output as
before the disturbance in only 2 hours, thus showing the effectiveness
of the controller in ensuring a consistent output with rapid response.
In addition, a real-time pooling strategy allowed adaptation of the
pooling absorbance cutoff levels to the size of the peak in the elution
of the polishing step.
It was shown that the continuous process outperformed the batch process,
with a productivity increase of 95% and a 28% higher yield.
Additionally, by comparing the integrated continuous process with and
without the controller after the concentration disturbance, it was found
that the amount of product loaded was lower in the process without the
controller, thus leading to a lower resin utilization and lower product
output. This, in turn, led to a higher specific buffer consumption than
in the process with the controller. The controller thus ensured similar
resin utilization and product output with and without the disturbance.
The whole downstream process was implemented in a two-system setup with
minimal use of resources and space. This process setup and the control
strategies developed could be used for any downstream process. This
configuration is thus well suited in a ballroom-like facility that
offers multi-product and multi-purpose manufacturing capabilities,
allowing quick responses to market demands.