Bcl‐xL mediates increased production of humanized monoclonal antibodies in Chinese hamster ovary cells

Abstract Enhanced product yields, reduction in throughput time, improved cost‐effectiveness and product quality are examples of benefits gained by delaying apoptotic cell death in bioreactors. To examine the effect on recombinant protein production, bcl‐x L was overexpressed in a CHO cell line secreting humanized monoclonal antibody directed against the α1β1 integrin. When cell lines overexpressing bcl‐x L were compared to the parent, cell viability was increased by 20% and titers by 80%. Total viable cell densities were similar and specific productivities were enhanced by almost two‐fold on scale‐up to bioreactors. Comparison in a chemically defined media demonstrated an even greater sustained viability in bcl‐x L expressing cells by 50% and up to 90% increase in titer with no impact on product quality. Caspase 3 activities were monitored as a marker for apoptotic cell death. In the presence of Bcl‐x L , caspase activities were reduced to background levels. The role of Bcl‐x L in protecting cells from premature death was further examined in studies performed in the presence of NaBu, at concentrations known to trigger cell death. Results demonstrated that cells expressing bcl‐x L retained 88% cell viability with >2 fold increase in titer. Bcl‐x L was similarly overexpressed in a different CHO cell line producing a humanized mAb against the chemokine MCP1. Once again, production titer was increased by 80% and viability by 75%. Together the studies have shown that overexpression of bcl‐x L in production cell lines was able to significantly increase the titer by enhancing both the specific activity and total cell viability while maintaining product quality. © 2005 Wiley Periodicals, Inc.