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 (S FV) vector and high titer recombinant SFV particles generated. The broad ho st range of SFV allowed efficient infection and high level expression of fo ur mammalian cell lines growing in serum-free suspension cultures. The incu bation temperature had dramatic effects on the level and duration of recomb inant protein expression. For example, the luciferase activity was signific antly 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 cultu res incubated at 37 degrees C. Only a slight temperature effect on lucifera se expression was seen in the human cell line HEK293 and no effect was obse rved for the subclone293(EBNA).