Background: After intravenous delivery of the adenoviral vector into rats or mice, 95-99% of the encoded protein is produced in the hepatocytes. We observed, as have others, that the early expression levels of the vector encoded protein vary, greatly, within a species, from one animal strain to another. This study was initiated to determine the molecular mechanism causing the difference: hepatic transfection, transcription or translation. For this purpose different doses of Ad5 luciferase and Ad5 LacZ were intravenously injected into Brown Norway rats and Wag/Rij rats, two strains that differ by a factor of 10 in encoded protein levels. The proportion of LacZ positive hepatocytes, the adenoviral DNA, specific transgenic RNA and luciferase protein were compared in the two strains.
Results: The number of transduced hepatocytes and the amounts of Ad5 DNA in the livers was similar in both strains, whereas the Brown Norway rats produced 8 to 10 times more of both vector encoded proteins and of transgene mRNA than the Wag/Rij rats.
Conclusions: It is concluded that the difference between strains in vector encoded protein expression is due to different transcriptional events. No evidence was obtained to suggest that the differences are related to liver damage influenced by vector toxicity or immune reactions.