Fiber shaft-chimeric adenovirus vectors lacking the KKTK motif efficiently infect liver cells in vivo

The molecular mechanisms governing the infectivity of adenovirus (Ad) toward specific cell and tissue types in vivo remain poorly understood. The direct Ad binding to hepatic heparan sulfate proteoglycans via the KKTK motif within the fiber shaft domain was suggested to be the major mechanism of Ad liver cell infection in vivo. Here, we describe the generation and in vitro and in vivo infectivity studies of Ad5-based vectors possessing long Ad31- or Ad41-derived fiber shaft domains, which lack the KKTK motif. We found that all the critical early steps of Ad infection, including attachment to the cellular receptor, internalization, and virus genome transfer into the nucleus, occurred with similar levels of efficiency for fiber shaft-chimeric vectors and unmodified Ad5. Upon intravenous delivery into mice, fiber shaft-chimeric vectors accumulated in liver tissue, transduced liver cells, and induced the production of proinflammatory cytokines (tumor necrosis factor alpha and interleukin-6) and the chemokine monocyte chemoattractant protein 1 at levels indistinguishable from those observed for Ad5. Thus, our data provide evidence that the Ad5 fiber shaft amino acid sequence does not play any substantial role in determining adenovirus infectivity toward hepatic cells in vivo. The data obtained contribute to improving our understanding of the molecular mechanisms determining Ad infectivity and biodistribution in vivo and may aid in designing novel Ad-based vectors for gene therapy applications.