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.