Be that as it may, CHO cells are still the dominant stable producer lines in the pharmaceutical industry. Yet because R&D material is principally generated in HEK293-based cells, so as to minimize the (real and perceived) post-translational modification dissimilarities between transiently and stably expressed genes, there has been a call to develop a viable large-scale CHO transfection platform as an alternative. Regulatory submissions, too, would be simplified by using a common host to generate both preclinical and clinical matter.
Yves Durocher, Ph.D., research officer at the National Research Council Canada, has been heeding the call. His lab has developed a simple and robust transfection process that allows CHO cells to compete with the ease of use and expression levels of 293 cells.
The automation-compatible process utilizes serum-free medium (facilitating the recovery of secreted proteins), does not require medium exchange prior to or following transfection, and makes use of suspension cells, allowing for scalability.
“We are basically using the same approach, same protocols, and the same vectors to transfect CHO cells,” he said. As such they typically express every new target in both 293 cells and CHO cells, and test lines in parallel for the best expression and product quality/activity.
In some cases there have been differences in glycans or other post-translational modifications between the two hosts, which can be critical for many biological functions. This can be the result of rodents expressing different enzymes and in different proportions than humans, or by the fact that ovary metabolism may differ from that of the kidney.
“The more hosts we have, I think, the better,” commented Dr. Durocher. “It provides you with other options for different targets.”
But all else being equal, Dr. Durocher thinks that companies that already have stable CHO expression platforms for manufacturing biologics would rather use a large-scale CHO transient transfection system than use different platforms for research and production.
For most of the small percentage of proteins that can’t be made in the cells as they are now, “you can still stay with CHO cells and just engineer them to provide better biologics,” he said. “But of course you also have the opportunity to switch hosts and start from scratch in developing a new platform.”