Impact of cellular stress on recombinant monoclonal antibody produced by high yielding Chinese Hamster Ovary (CHO) cell cultures in bioreactors

Chinese hamster ovary (CHO) cells are one of the most common cell line host for the production of recombinant proteins in biopharmaceutical industry. In order to ensure a continuous supply and meet an increasing market demand, bioprocess advances are needed where cells produce more product and are grown at higher cell densities. Under these conditions, cell energy requirements and the oxygen demand are increased and as a result more waste components are accumulated in the extracellular environment. Such conditions are more intensive and stressful for the cells and can lead to lower productivity, and eventually cell death. Thus, a control of cellular stress is required to maintain the recombinant production yields, product quality and to ensure the robustness of the bioprocess.

Overall, this PhD thesis focused on the understanding of oxidative stress to support future development of control strategies. In literature, oxidative stress is defined as the imbalance between oxidant molecules generation and antioxidant defense within the cells. Under bioprocess conditions, reactive oxygen species can be generated by multiple sources. In the first part, this thesis summarize the available knowledge on oxidative stress and gives an overview of strategies used to control it in CHO cells. The second part of this thesis covers an investigative study focusing on glutathione metabolism and its relationship with specific productivity. Based on a genome-wide proteomic analysis, we have identified a link between oxidative stress and cholesterol biosynthesis. In a second study, we have observed different responses depending on the oxidative stress sources. We have confirmed the link between oxidative stress and cholesterol biosynthesis and suggest a specific involvement of glutathione in the recombinant protein production. In the last part, the thesis ends on a case study where the modulation of oxidative stress using cystine analogs can help to improve product quality without detrimental effects on the process performance. Finally, we conclude and discuss future perspectives of the obtained results in this thesis.