Impact of cell lysis on the description of cell growth and death in cell culture.

The primary task of process development is a process design that guarantees product quality and maximizes product quantity. One part of the process development is the identification of critical process parameters. Especially in cell culture processes, unwanted cell damage as critical process parameter is still challenging in stirred tank reactors and needs therefore to be considered. Nevertheless, this topic and its effects on process performance are currently not well discussed and not verified in literature until now. The process of cell damage or lysis can be defined as the loss of integrity of the cells. For the investigation of this phenomenon, a model-based designed fed-batch cultivation with Chinese hamster ovary cells was performed. Besides measurements of viable and dead cell concentration, lysed cell count was determined by DNA measurements. Based on these analytics, different hypotheses, characterizing the cell death, were compared. From this, four main statements could be derived: (i) consideration of lysis in cell culture processes is of great importance for the description of the living biomass population in terms of growth and dying; (ii) a higher effort in process monitoring facilitates significantly model development; (iii) in contradiction to existing models from literature, our verification approach demonstrated a direct correlation of lysis with viable cell concentration and therefore with productivity; and (iv) lysis could be effectively described by only one model parameter, the specific lysis rate from viable cells to lysed cells. All these statements could be accurately proven by statistical methods. Our results enable future detailed investigations of the causes of cell damage and the influences of cell lysis on product quality and quantity. Potential application fields are scale-up issues, process optimization, and impurity screening.