Screening of transformed insect cell lines for recombinant protein production

Nine insect cell lines were evaluated for their potential as host systems f or recombinant protein production using a new expression vector permitting the continuous high-level expression of secreted glycoproteins by transform ed insect cells (Farrell et al., 1998). As a means of preliminary screening , all nine insect cell lines were transfected with the green fluorescence p rotein. Growth in static and suspension culture was then examined as a furt her method of screening. On the basis of their transfection efficiencies an d cell growth characteristics, five insect cell lines, Bm5, High Five, IPLB -LdFB, IZD-MB-0503, and Sf-21, were selected for stable transformation to p roduce granulocyte-macrophage colony-stimulating factor (GM-CSF). These fiv e cell lines were stably transformed using an antibiotic resistance scheme and evaluated as a polyclonal population. Increasing the antibiotic concent ration was found to cause not only a decrease in the specific growth rate b ut also an increase in the specific protein production rate and final GM-CS F concentration. The transformed High Five cells exhibited by far the great est specific protein production rate of 5.1 x 10(-6) mu g/(cell.h), resulti ng in the highest final GM-CSF concentration of 22.8 mg/L when grown in sta tic culture. One cloned High Five cell line produced a GM-CSF concentration of 46 mg/L in static culture and 27 mg/L in suspension culture.