Production methods of recombinant proteins; towards mastering glycosylation

In 2009, the Food and Drug Administration (FDA) and the European Agency for the Evaluation of Medicinal Products (EMEA) granted marketing authorization to more than 150 recombinant proteins, known as "biopharmaceuticals". Of these, 76 were produced using mammalian cells. Notwithstanding much higher protein concentrations and much lower processing constraints, bacterial expression systems do not allow complex post-translational modifications (PTMs), unlike animal and mammalian cells in particular. Of these, glycosylation is the most important; it is present on over 50% of human proteins, and confers functional, structural and pharmacokinetic properties on the proteins that carry them. Whereas glycosylation is not ensured by bacterial systems, or is only partially ensured by yeast or insect cells, mammalian cells, and CHO cells in particular, have gradually emerged as the expression hosts of choice for the production of complex recombinant proteins of therapeutic interest. In addition to glycosylation, protein production in this cell system has the advantage of generally being able to perform other important TPMs, including sulfation and proteolysis.

The aim of this article is to describe, in general terms, the different cell systems used by the biotechnology industry and the main qualitative characteristics of recombinant proteins. Particular emphasis is placed on post-translational modifications, primarily glycosylation. The description of the cellular mechanisms involved in protein glycosylation, of the different production methods and of the choice of operating parameters represents an essential knowledge base for the implementation of new production processes or the targeted improvement of existing ones.