Advances in animal cell recombinant protein production: GS-NS0 expression system

The production of recombinant proteins using mammalian cell expression syst ems is of growing importance within biotechnology, largely due to the abili ty of specific mammalian cells to carry out post-translational modification s of the correct fidelity. The Glutamine Synthetase-NS0 system is now one s uch industrially important expression system. Glutamine synthetase catalyse s the formation of glutamine from glutamate and ammonia. NS0 cells contain extremely low levels of endogenous glutamine synthetase activity, therefore exogenous glutamine synthetase can be used efficiently as a selectable mar ker to identify successful transfectants in the absence of glutamine in the media. In addition, the inclusion of methionine sulphoximine, an inhibitor of glutamine synthetase activity, enables further selection of those clone s producing relatively high levels of transfected glutamine synthetase and hence any heterologous gene which is coupled to it. The glutamine synthetas e system technology has been used for research and development purposes dur ing this decade and its importance is clearly demonstrated now that two the rapeutic products produced using this system have reached the market place.