4. Conclusion and future prospects
The cyclical semicontinuous operation in a pilot-scale bioreactor using simplified bioreactor processing yielded consistent maximum total active rrBChE production levels in the four cycles over 82-days of operation showing the potential robustness and stability of the transgenic rice cell cultures for rrBChE production. Here, in best of our knowledge for the first time, we report the longest plant cell culture bioreactor with reproducible production of a plant-made therapeutic recombinant protein in a pilot-scale bioreactor. Using kLa as a scale-up parameter, the pilot-scale batch culture without baffles provides comparable growth kinetics, maximum total rrBChE production level, maximum volumetric productivity and maximum specific productivity as obtained from the lab-scale bioreactor. Based on Western blot analysis, the culture medium rrBChE is likely the extracellular rrBChE that is secreted to the medium via the secretory pathway guided by the RAmy3D signal peptide. Altogether, we demonstrate a simple, reproducible, and scalable platform for rrBChE production.
Future work will investigate medium optimization to improve rrBChE production level and productivities. A cyclical semicontinuous pilot-scale bioreactor operation without baffles and simplified bioreactor processes using kLa as a scale-up parameter is worth studying in a long-term operation (>6 months). Exploring strategies and methods to mitigate bioreactor wall growth of cell aggregates and cell lysis is also needed in a long-term semicontinuous bioreactor operation reported as a better cost-effective operation than batch operation for plant cell-made biopharmaceuticals (Corbin et al., 2020).