Effect of temperature on recombinant protein expression in Semliki Forest virus infected mammalian cell lines growing in serum- free suspension cultures

The firefly luciferase gene was introduced into the Semliki Forest virus (SFV) vector and high titer recombinant SFV particles generated. The broad host range of SFV allowed efficient infection and high level expression of four mammalian cell lines growing in serum-free suspension cultures. The incubation temperature had dramatic effects on the level and duration of recombinant protein expression. For example, the luciferase activity was significantly higher in the rodent BHK and CHO cell lines incubated at 33 degrees C compared to 37 degrees C when harvested 19 h post-infection. At 33 degrees C the specific expression levels increased 10-20 fold during prolongation of the post-infection time up to 50 h. In contrast, a significant decrease in luciferase activity was observed from 26 h post-infection for cell cultures incubated at 37 degrees C. Only a slight temperature effect on luciferase expression was seen in the human cell line HEK293 and no effect was observed for the subclone293(EBNA).