Abstract
Expression of human interleukin 2 (IL-2) at high levels has been achieved in human cells by cotransfection and subsequent coamplification of the transfected sequences. IL-2 production by these cells reached 2700 U/ml of culture medium. This productivity was higher than the 100U/ml attained by concanavalin A (ConA) stimulated human leukaemic Jurkat, T cells. A plasmid, pSDI, containing human IL-2 cDNA and mouse dihydrofolate reductase (DHFR) cDNA was constructed, and cotransfected with plasmid pSV2neo at a 10:1 molar ratio, into Hela (human epitheloid carcinoma) cells by the DNA-calcium phosphate coprecipitation technique. Transformants producing IL-2 were easily obtained among antibiotic G418 resistant colonies. Cells resistant to increased levels of methotrexate (MTX) secreted a large amount of IL-2 as a result of coamplification of DHFR cDNA and IL-2 cDNA. Expression of IL-2 cDNA was stimulated by removing a G-C stretch which was present between Simian Virus 40 (SV40) early promoter and IL-2 cDNA. Plasmid pSDI was rescued from the transformed Hela cells and shown to be present in the intact form among the amplified cellular DNA.
