Anti-apoptotic genes Aven and E1B-19K enhance performance of BHK cells engineered to express recombinant factor VIII in batch and low perfusion cell culture

Abstract

The engineering of production cell lines to express anti‐apoptotic genes has been pursued in recent years due to potential process benefits, including enhanced cell survival, increased protein expression, and improved product quality. In this study, a baby hamster kidney cell line secreting recombinant factor VIII (BHK‐FVIII) was engineered to express the anti‐apoptotic genes Aven and E1B‐19K. In high cell density shake flask culture evaluation, 11 clonal cell lines expressing either E1B‐19K or a combination of Aven and E1B‐19K showed improved survival compared to both parental and blank vector cell line controls. These cell lines exhibited lower caspase‐3 activation and reduced Annexin‐V binding compared to the controls. Parental and blank vector cell lines were less than 50% viable after 48 h of exposure to thapsigargin while cell lines expressing E1B‐19K with or without Aven maintained viabilities approaching 90%. Subsequently, the best Aven‐E1B‐19K candidate cell line was compared to the parental cell line in 12‐L perfusion bioreactor studies. Choosing the appropriate perfusion rates in bioreactors is a bioprocess optimization issue, so the bioreactors were operated at sequentially lower specific perfusion rates, while maintaining a cell density of 2 × 10 7 viable cells/mL. The viability of the parental cell line declined from nearly 100% at a perfusion rate of 0.5 nL/cell/day to below 80% viability, with caspase‐3 activity exceeding 15%, at its lower perfusion limit of 0.15 nL/cell/day. In contrast, the Aven‐E1B‐19K cell line maintained an average viability of 94% and a maximum caspase‐3 activity of 2.5% even when subjected to a lower perfusion minimum of 0.1 nL/cell/day. Factor VIII productivity, specific growth rate, and cell size decreased for both cell lines at lower perfusion rates, but the drop in all cases was larger for the parental cell line. Specific consumption of glucose and glutamine and production of lactate were consistently lower for the Aven‐E1B‐19K culture. Furthermore, the yield of ammonia from glutamine increased for the Aven‐E1B‐19K cell line relative to the parent to suggest altered metabolic pathways following anti‐apoptosis engineering. These results demonstrate that expression of anti‐apoptotic genes Aven and E1B‐19K can increase the stability and robustness of an industrially relevant BHK‐FVIII mammalian cell line over a wide range of perfusion rates. Biotechnol. Bioeng. 2007; 98: 825–841. © 2007 Wiley Periodicals, Inc.