A scale-down approach to assess scale-up induced process variability in mammalian cell culture

Abstract

A great share of biopharamceutical products is nowadays derived from mammalian cell cultivations. However, the scale-up of cell culture processes is a challenging task, often resulting in variable process performances across the scales. Due to the nature of bioreactor scale-up it is impossible to maintain all operational conditions equal between small-scale and large-scale cultivations. Variations in operational parameters can lead to a physiochemical variability with direct influence on cell specific physiological conditions, finally altering product quality and process performance. The goal of this thesis was to evaluate the impact of large-scale inhomogeneities, that arise during process scale-up, on cell physiology and process performance using a scale-down approach. Hereby physiological effects of large-scale inhomogeneities were uncovered through application and combination of a decoupled control strategy for process parameters (pH, pO2 and pCO2) with multivariate data analysis as well as metabolic flux analysis and the establishment of a two-compartment bioreactor system. Through this methodology novel process parameter interaction effects as well as intracellular metabolic regulations were revealed. Furthermore, the development and application of the two-compartment bioreactor system led to an improved understanding of the impact of temporary pH gradients on cell physiology and process performance. The gathered results demonstrate that the used scale-down approach in combination with appropriate investigative methods is capable of revealing novel effects that might occur during large-scale mammalian fermentation processes. The transferability of these obtained results back to the large-scale is however challenging due to the lack of knowledge of the actual large-scale conditions.