CHO Cells Explained

Many non-scientists who work in the biotech industry have heard of CHO cells, and know that they are a cell line commonly used to manufacture biologic drugs. But what are these ubiquitous CHO cells?

CHO stands for Chinese Hamster Ovary. This means that this cell line was derived from the cells of a Chinese hamster – a particular breed of hamster that originated in the deserts of Northern China and became a common animal model for the typing of pneumococci in the early 20th century. In the 1950s, scientists began deriving cell lines from these hamsters, and found that they grew well in tissue culture, demonstrating resiliency and relatively fast generation times. This made them an invaluable tool for a host of areas of basic science research ranging from genetics to cancer biology.

Twenty years later, when the biotechnology revolution began and scientists began to use cells to make therapeutic proteins in large quantities, the first cell type used was the bacterial cell E. coli, used to produce human insulin by Genentech scientists. Although E coli worked well for relatively simple proteins such as insulin, as researchers began to explore the possibility of producing other, more complex proteins as therapeutics, it became clear that another cell type was needed. Bacterial cells are simply not capable of producing complex human proteins in the correctly folded and post-translationally modified form required for a human therapeutic.

The obvious choice for human therapeutic protein production was some sort of mammalian cell. Why not a human cell line? It turns out that human cell lines are relatively difficult to keep alive in cell culture. They simply do not survive and multiply as well as rodent cell lines such as CHO cells. Decades of experience with CHO cells had taught scientists that these cells were not only easy to grow in culture, but could also be adapted to grow in liquid suspension cultures to high volumes – a very important trait when considering the production of biologics. CHO were also found to be capable of taking up foreign genetic material. Finally, these cells are safe for the production of human therapeutics – in fact, they are probably safer than an actual human cell line would be, because most human pathogenic viruses, including HIV, influenza, herpes, and measles, do not infect these cells. From a regulatory perspective, CHO cells have stood the test of time and have a special status – Generally Regarded As Safe (GRAS).

The first human therapeutic to be produced in CHO cells was Activase, a recombinant version of the human protein tissue plasminogen activator used in the treatment of acute myocardial infarction. Activase was approved in 1987. Since that time, CHO cells have been used to produce dozens of other life-saving biologics. For all of these reasons – ease in growing to large volumes, ability to manipulate genetically, and a proven track record in producing safe human therapeutics – we can expect CHO cells to remain a favorite workhorse of the biotech industry.