(191ad) A Segregated Kinetic Model for Antibody Producing Cell Lines

Authors: 
Yilmaz, D., Illinois Institute of Technology
Parulekar, S. J., Illinois Institute of Technology
Cinar, A., Illinois Institute of Technology
Monoclonal antibodies (MAbs) have extensive biomedical applications, account for nearly 40% of the sale of biologics in the U.S., and are produced in animal cell bioreactors at a variety of scales. Mammalian cell cultures have become the favored production hosts for MAbs, since microbial systems are not able to carry out the complex post-translational and functional modifications of these proteins, such as glycosylation. The efficiency and performance of these cell cultures require use of highly specialized culture media to enhance MAb yield in in vitro production, since the cells are subject to death and a considerable understanding of the variations in MAb productivity due to variations in culture conditions.

Cell death is a key issue in the bioreactor culture, as it decreases overall cell yield. Death of mammalian cells occurs mainly in two distinct forms: uncontrolled cell death (necrosis) and programmed cell death (apoptosis). Necrosis is a sudden and passive form of cell death, caused by cell membrane damage occurring upon extreme environmental stress, such as high shear stress on the cell membrane as a result of collision with the bioreactor walls or stirrers, exposure to high levels of toxic metabolites or any environmental insult. Apoptotic death can account for up to 80% of mammalian cell death in bioreactors, which restricts cell growth and viability and ultimately decreases cell yield. Therefore, apoptosis has been considered as a target to maintain high cell culture viability and increase antibody production in many prior research studies.

Based on metabolic flux analysis (MFA), a segregated modeling approach is presented in this work for MAb production by hybridoma cells. The viable cell population is segregated into
growing and apoptotic subpopulations to predict more precisely the effect of culture conditions on cell growth, cell death and target product formation. The MFA-based model is developed based on a set of key macro-reactions and considering effect of specific growth rate on production and consumption rates of extracellular nutrients and metabolites. The cell-specific kinetics of growth are expressed in terms of concentrations of glucose, glutamine, lactate, and ammonia. The integrated model predicts the temporal profiles of concentrations of essential nutrients, key metabolites and the cell populations for specific initial culture conditions for batch and fed-batch cultures. The segregation of the cell population enables the quantitative assessment of apoptotic state of the cell culture, impact of apoptosis and necrosis, and distribution of MAb production among growing and non-growing cells. The overall productivity is indirectly affected by the apoptotic state of the culture since the apoptotic state determines the overall cell viability. The model predictions compare well with the experimental data for many batch and extended batch experiments.