The accumulating dogma seems to indicate that CMV expresses in a number of cell types. For example, CMV drives expression in frog oocytes. The following articles discuss the CMV promoter in S2 cells. One provides evidence that it works well and one finds that it does not. Indicates that CMV promoter does not work in Kc1 and S2 cells: Gene 1997 Apr 1;188(2):183-90 Pfeifer TA, Hegedus DD, Grigliatti TA, Theilmann DA Baculovirus immediate-early promoter-mediated expression of the Zeocin resistance gene for use as a dominant selectable marker in dipteran and lepidopteran insect cell lines. Demonstrates that CMV promoter does work in Drosophila cells: Nucleic Acids Res 1987 Mar 11;15(5):2392 Sinclair JH The human cytomegalovirus immediate early gene promoter is a strong promoter in cultured Drosophila melanogaster cells.