Approaches to maximizing stable expression of alpha 1-antitrypsin in transformed CHO cells

A variety of approaches to maximizing the production of recombinant human alpha 1-antitrypsin (AAT) in Chinese hamster ovary (CHO) cells have been investigated. The highly active and inducible human cytomegalovirus immediate early (IE) promoter/enhancer was used to drive transcription of a recombinant AAT gene in transiently transfected and stably transformed CHO cells. The AAT gene was modified to incorporate highly efficient 3'RNA processing signals from the herpes simplex virus type 2 IE gene 5, and optimal translational initiation signals were created by site-directed mutagenesis. The effect of flanking the recombinant gene with matrix attachment regions was investigated. Combinations of these modifications allowed secretion of up to 44 micrograms AAT/ml per day by cell lines growing in serum-rich medium. This could be increased to up to 100 micrograms AAT/ml per day upon chemical induction of expression by propionate, butyrate or hexamethylene bisacetamide. Cell lines adapted to grow in protein-free medium produced less AAT but still responded to chemical induction to secrete up to 14 micrograms/ml per day of readily purified AAT.