Comparison of the human versus murine cytomegalovirus immediate early gene promoters for transgene expression by adenoviral vectors.

We have developed a number of replication defective adenoviral (Ad) vectors which express transgenes under the control of the human cytomegalovirus (HCMV) immediate early (IE) gene promoter. The orientation of the expression cassette replacing E1 in the vector backbone had a significant effect on the level of transgene expression, with vectors containing expression cassettes directed towards the right end of the Ad genome expressing 7-fold higher levels of beta-galactosidase (beta-gal) than those with inserts in the opposite orientation. Murine cells infected with any of several different Ad vectors in which transgene expression was under the control of the HCMV IE promoter produced 10-100-fold less transgene product (such as beta-gal) than similarly infected human cells. Replacing the HCMV IE promoter with the murine CMV (MCMV) IE promoter resulted in an increase in the levels of beta-gal produced in murine and rat cells by approximately 5-30-fold compared to levels obtained with the HCMV IE promoter, and levels produced in human cells were the same or greater using the MCMV IE promoter compared to the HCMV IE promoter. Similar results were obtained using a luciferase reporter gene. The MCMV IE promoter, therefore, was able to drive high levels of expression without the pronounced species preferences observed for the HCMV IE promoter. The MCMV IE promoter also directed high levels of expression in vivo, suggesting that Ad vectors carrying the MCMV IE promoter may be more effective than those with the HCMV IE promoter for transgene expression in animal models.