P115: Scale Down of Recombinant Protein Expression in Saccharomyces cerevisiae to 3-L scale

The development of a scale down system became necessary to allow for expanded experimental capacity in support of a recombinant Saccharomyces cerevisiae process. An established 20-L scale system was used as a baseline to compare process outputs at 3-L scale. The fermentation process consists of batch, fed batch and protein-induction phases with metabolism and process attributes being compared across scales for each of the phases. Key process parameters that would be compared across scales were dissolved oxygen, pH, OUR, CER, cellular metabolism and product attributes. Initial experiments were run at baseline conditions with agitation being scaled down by matching power per volume. Both DO profiles and induction phase metabolism were observed to be different between scales. One key difference between these two systems lies in the OTR that can be achieved with agitation, oxygen blending and back pressure. With no back pressure controller available in the 3-L system, impeller design and agitation were modified to match DO profiles more closely across scales. Special emphasis was given to match profiles during the batch and fed-batch phases as each was known to impact process outputs during protein production stage. Another important variable was determined to be media sterilization parameters with initial experiments using media steamed in place at large scale. To fully develop an independent 3-L model SIP parameters, including heat times, had to be modeled in an autoclave cycle. The 3L scale-down model was used successfully for process development activities.