Intravenous readministration of an adenoviral vector performed long after the initial administration failed to induce re-expression of the original transgene in rats

Although most humans have been exposed to wild-type adenoviruses in their c hildhood, titers of neutralizing antibodies against viruses decrease with t he passage of time. In the present study, we infused adenoviruses carrying the lacZ gene into the tail vein of rats, and re-infused the same adenoviru ses long after the initial administration. However, development of neutrali zing antibodies against adenovirus and proliferation of adenovirus-specific T cells were elicited profoundly by adenoviral readministration, and trans gene expression was not induced in rats. Our results may have important imp lications for efficacy considerations when adenoviral vectors are employed in clinical settings for the treatment of cancer.