John Birch, Ph.D., CSO at Lonza (www.lonza.com), discussed his group’s efforts to improve protein synthesis capability in the CHO cell line. Manipulation of nutritional conditions, optimization of feeding strategy, and the engineering of the genetic makeup of a particular cell isolate are the critical inputs in maximizing protein production.
In the last 40 years there have been numerous protein-free and serum-free media developed for the CHO line. The Lonza group has focused its efforts on completely protein-free media and feeds for its fed-batch culture systems. As the technology has improved, there have been increases of orders of magnitude, bringing yields in the range of grams per liters. The drivers of these advances are augmentation in cell density and enhancement in per cell protein production. As the technology matured, Lonza realized a 167-fold boost between 1990 and 2008, according to Dr. Birch.
In one series of trials, Lonza scientists isolated a variant, the CHOK1SV cell line, that achieved higher cell concentrations and maintained viability longer than another commonly used line (the CHO DG44) when grown under the same conditions. Dr. Birch strived for a simplified screening system that would allow processing of many clones with different genetic backgrounds.
“We have aimed at a straightforward screening regime,” Dr. Birch stated. “We use the GS expression system, which has a high level of selection stringency, and we have started with the CHOK1SV cell line, which has improved growth characteristics.”
A particularly favorable property of the cell line is its anchorage-independent growth properties. Ordinarily, CHO cell lines grow attached to the culture vessel, presumably due to the production of adhesive proteins. By selecting for a strain that grows in suspension, the Lonza workers were able to improve performance and save time during the developmental process. Using a relatively simple screening program, the Lonza group is able to routinely generate highly productive cell lines making grams per liter of antibody.
For Dr. Birch, the take-home message is that the optimal approach to improving protein output is based on ratcheting up a cell’s capacity for protein synthesis. “To do this you need to understand the biological underpinnings of cell performance and perfect your tools for assessing the functional capabilities of the cells,” he posited.