Evaluation of promoters for foreign gene expression in the E3 region of bovine adenovirus type-3

In order to optimize foreign gene expression in the E3 region of BAdV-3, we constructed full-length BAdV-3 genomic DNA clones containing a reporter gene (truncated glycoprotein gD of bovine herpesvirus 1, gDt), under the control of exogenous promoters inserted in either direction in the E3 region. Irrespective of exogenous transcriptional elements, viable recombinant BAdV-3 viruses could only be isolated when the gDt expression cassettes were inserted in the E3 region parallel to the direction of E3 transcription. Introduction of exogenous promoters altered the kinetics and amount of gDt expression in recombinant BAdV-3 infected cells. Interestingly, recombinant BAdV-3 containing gDt under the control of the mouse cytomegalovirus (MCMV) immediate early (IE) promoter expressed gDt more efficiently with noticeable differences in the amount and kinetics of expression. Moreover, animals immunized with recombinant BAdV-3 expressing gDt under the control of the MCMV IE promoter induced strong immune responses with reduced pathological lesions. These results suggest that BAdV vectors with the MCMV IE promoter may be useful for transgene expression and the development of vaccines.