Expression of Coxsackie adenovirus receptor and alphav-integrin does not correlate with adenovector targeting in vivo indicating anatomical vector barriers

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Abstract
Recombinant adenoviral vectors are broadly applied in gene therapy protocols. However, adenovector-mediated gene transfer has limitations in vivo. One of these is the low gene transfer rate into organs other than the liver after systemic intravenous vector injection. Local direct injection into the target organ has been used as one possible solution, but increases necessary equipment and methodology and is traumatic to the target. Wild-type adenovirus infection as well as adenovector-mediated gene transfer depends on virus interaction with the Coxsackie adenovirus receptor (CAR) mediating virus attachment to the cell surface, and on interaction with αvβ3 and αvβ5 integrins mediating virus entry into the cell. In order to assess the receptor-associated potential of different tissues to act as adenovector targets, we have therefore determined CAR and αv-integrin expression in multiple organs from different species. In addition, we have newly determined several human, rat, pig and dog CAR-mRNA sequences. Sequence comparison and structural analyses of known and of newly determined sequences suggests a potential adenovirus binding site between amino acids 29 and 128 of the CAR. With respect to the virus receptor expression patterns we found that CAR-mRNA expression was extremely variable between different tissues, with the highest levels in the liver, whereas αv-integrin expression was far more homogenous among different organs. Both CAR and αv-integrin showed similar expression patterns among different species. There was no correlation, however, between the adenovector expression patterns after intravenous, intracardiac and aortic root injection, respectively, and the virus receptor patterns. In summary, many organs carry both receptors required to make them potential adenovector targets. In sharp contrast, their actual targeting clearly indicates that adenovirus receptor expression is necessary but not sufficient for vector transfer after systemic injection. The apparently very important role of anatomical barriers, in particular the endothelium, requires close attention when developing non-traumatic, organ-specific gene therapy protocols.