Expression of Recombinant Antibodies

Frenzel, André; Hust, Michael; Schirrmann, Thomas

Today, 60-70% of all recombinant protein pharmaceuticals and 95% of the currently approved therapeutic antibodies are still produced in mammalian cell lines despite relatively high production costs and difficult in handling. However, the advanced mammalian folding, secretion and post-translational apparatus is capable of producing antibodies indistinguishable from those in the human body with least concerns for immunogenic modifications. Moreover, it is also highly efficient for secretion of large and complex IgGs and in combination with the folding and post-translational control it results in high product quality which reduces efforts and costs in the subsequent and more expensive downstream processing steps. The risks of contamination by pathogens or bovine spongiform encephalopathy (TSE/BSE) agents have been eliminated by well-documented Good Manufacturing Practice (GMP) compliant designer cell substrates and chemical defined media without the need of supplementing animal serum components (145) . In 2004, mammalian cell culture technology reached production levels of approximately 5 g/L IgGs in Chinese hamster ovary (CHO) cells (146). Today, industrial IgG production levels often exceed 12 g/L as the result of a steadily ongoing progress in mammalian cell culture technology, which is mainly due to improved high producer cell lines, optimized production media, and prolonged production processes at high-cell densities. The highest reported IgG production titer we found was obtained in the human embryonic retinal cell line Per.C6 [Crucell, Leiden, Netherlands, (147)] with 27 g/L. Generally, the productivity of recombinant mammalian cell lines increased from initially 10 pg antibody per cell per day (pcd) in 1986 to about 90 pcd in 2004. Today, the antibody production levels only rarely exceed 100 pcd because higher cellular productivity usually corresponds to lower maximum cell densities in the production process. Producer cell lines have also been genetically engineered regarding product homogeneity, improved metabolism, reduced apoptosis, and inducible cell cycle arrest (148, 149) which allows prolonged production times for almost 3 weeks at high-cell viability and cell densities.