Expression of pIX gene induced by transgene promoter: possible cause of host immune response in first-generation adenoviral vectors.
First-generation (FG) adenoviral vectors (AdVs) have been widely used not only for gene therapy but also for basic studies. Because vectors of this type lack the E1A gene that is essential for the expression of other viral genes, their expression levels in target cells have been considered low. However, we found that the viral pIX gene, located immediately downstream of the inserted expression unit of the transgene, was significantly coexpressed with the transgene in cells infected with FG AdV. Whereas CAG and SRalpha promoters activated the pIX promoter considerably through their enhancer effects, the EF1alpha promoter hardly did. Moreover, when the expression unit was inserted in the rightward orientation, not only the pIX protein but also a fusion protein consisting of the N-terminal part of transgene product and pIX were sometimes coexpressed with the transgene product through an aberrant splicing mechanism. In in vivo experiments, a LacZ-expressing AdV bearing the CAG promoter caused an elevation of alanine aminotransferase, but an AdV bearing the EF1alpha promoter produced no detectable levels. Whereas the FG AdV expressing human growth hormone under the control of the CAG promoter maintained a high hormone level for less than 1 month, the FG AdV under the control of the EF1alpha promoter maintained a high level for at least 6 months. These results suggest that pIX coexpression may be one of the main causes of AdV-induced immune responses, and that the EF1alpha promoter is probably valuable for the long-term expression of FG AdV. Thus, the in vivo utility of FG AdV should be reevaluated.
Nakai
Michio
M
Drug Research Division, Dainippon Sumitomo Pharma, Osaka 554-0022, Japan.
Komiya
Kazuo
K
Murata
Masashi
M
Kimura
Toru
T
Kanaoka
Masaharu
M
Kanegae
Yumi
Y
Saito
Izumu
I
D000260:Adenoviruses, Human / Q000235:genetics*; D000410:Alanine Transaminase / Q000097:blood; D000818:Animals; D015153:Blotting, Western; D036022:Capsid Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D045744:Cell Line, Tumor; D004742:Enhancer Elements, Genetic; D005260:Female; D018014:Gene Transfer Techniques; D015316:Genetic Therapy; D005822:Genetic Vectors; D019382:Human Growth Hormone / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000276:immunology; D051379:Mice; D011401:Promoter Regions, Genetic; D019076:Transgenes
D036022:Capsid Proteins; C018315:hexon capsid protein, Adenovirus; D019382:Human Growth Hormone; D000410:Alanine Transaminase