Downstream processing of proteins from mammalian cells.

Less than a decade ago, the use of continuous mammalian cell lines for the production of cloned proteins was considered strictly a research tool. At that time, few thought it possible to allay the many safety concerns associated with transformed cells. It soon became clear that mammalian expression systems had numerous advantages over bacteria for production of therapeutic proteins, initiating a multidisciplinary effort to address these concerns in a thorough and reliable manner. The success of these efforts is exemplified by the emergence of product molecules into the market. Today, there are seven recombinant human therapeutics that have received FDA approval. Almost half of them (OKT3, t-PA, and EPO) are produced in mammalian cells, with the remainder produced in bacteria (insulin, growth hormone, and alpha-interferon) or yeast (hepatitis vaccine). At least a dozen more recombinant cell culture products are in advanced human clinical trials. With the accumulation of data and experience, continuous mammalian cell lines will no doubt be the preferred hosts for many future products of biotechnology.