Abstract
Monoclonal antibodies are commercially important, high value biotherapeutic drugs used in the treatment of a variety of diseases. These complex molecules consist of two heavy chain and two light chain polypeptides covalently linked by disulphide bonds. They are usually expressed as recombinant proteins from cultured mammalian cells, which are capable of correctly modifying, folding and assembling the polypeptide chains into the native quaternary structure. Such recombinant cell lines often vary in the amounts of product produced and in the heterogeneity of the secreted products. The biological mechanisms of this variation are not fully defined. Here we have utilised experimental and modelling strategies to characterise and define the biology underpinning product heterogeneity in cell lines exhibiting varying antibody expression levels, and then experimentally validated these models. In undertaking these studies we applied and validated biochemical (rate-constant based) and engineering (nonlinear) models of antibody expression to experimental data from four NS0 cell lines with different IgG4 secretion rates. The models predict that export of the full antibody and its fragments are intrinsically linked, and cannot therefore be manipulated individually at the level of the secretory machinery. Instead, the models highlight strategies for the manipulation at the precursor species level to increase recombinant protein yields in both high and low producing cell lines. The models also highlight cell line specific limitations in the antibody expression pathway.
Highlights
Mammalian cell lines have been used industrially for several decades for the production of complex, high value recombinant therapeutic proteins
The detailed characterisation of recombinant protein expression systems is essential for understanding differences between expression cell lines and for the rational design of consistent and stable high producers
While this characterisation is relatively straightforward for single-protein products [40], it is complicated for products with more complex assembly pathways such as monoclonal antibodies
Summary
Mammalian cell lines have been used industrially for several decades for the production of complex, high value recombinant therapeutic proteins. As the demand for such protein based therapies has increased, so have the yields obtained from mammalian expression systems, with current product yields more than a 100-fold greater than those achieved 20–30 years ago [2,3,4]. Most of this increase in yield has come through improvements in culture media composition and feeding regimes [2], and/or via improved screening strategies to identify cell lines that obtain and maintain higher biomass [5].
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