Table I.

Advantages and disadvantages of different expression systems for scFvs

Expression system	Advantages	Disadvantages
Bacterial expression (E.coli)	Fast and easy Inexpensive Upscaling feasible High yields (≤2 g/l) for cytoplasmic expression	Endotoxin levels high Refolding necessary for inclusion bodies Yields depend on individual amino acid sequence No glycosylation possible No ER quality control
Yeast expression (Saccharomyces cerevisiae, Kluyveromyces lactis, Pichia pastoris)	No endotoxin Relatively inexpensive High yields Glycosylation possible	Upscaling more complicated than for bacteria Need patent license to make yeast glycans suitable for therapeutic applications
Plants	No endotoxin Upscaling feasible Glycosylation possible High yields	High technical hurdles Need patent license to make yeast glycans suitable for therapeutic applications
Insect cells	No endotoxin Glycosylation possible Upscaling feasible	ER quality control insufficient (baculovirus) Unsuitability of insect glycans for therapeutic applications
Mammalian cells	No endotoxin Glycosylation possible Mammalian glycosylation type	Moderate yields Upscaling difficult Secretion problems of certain antibody sequences