Characterization of recombinant glycosylated human interleukin 2 produced by a recombinant plasmid transformed CHO cell line

A recombinant plasmid containing expression units for human pre-interleukin 2 (pre-IL-2) and the selectable marker mouse DHFR, was constructed and used to transform DHFR − CHO cells to the DHFR + phenotype. Selected colonies were isolated and tested for IL-2 production. Twelve highly IL-2-producing clones were amplified in stepwise increasing concentrations of methotrexate. The IL-2 secreted into the culture medium by one of these clones was purified to homogeneity and partially characterized. N-terminal sequence analysis showed that pre-IL-2 was correctly processed during secretion. SDS gel electrophoresis and chromatofocusing experiments in conjunction with neuraminidase treatment indicated a posttranslational glycosylation of the secreted mature protein similar to that described for the tetrasaccharide structure of the N2 form of natural IL-2. This recombinant IL-2 has a specific activity of 2.5 × 10 7 U/mg.