Transient expression in mammalian cell lines is the most sought after method for production of  eukaryotic recombinant proteins and antibodies because of the following reasons

• Check proper folding of the expressed proteins.
• Test for corect disulfide bond formation.
• Has the ability to perform complex  post translational modifications (mainly glycosylation).
• Pilot scale evaluation of expression and optimization before scale-up.
• Ideal for drug discovery projects and experiments where protein activity and folding are crucial.