Subgroup B and F Fiber Chimeras Eliminate Normal Adenovirus Type 5 Vector Transduction In Vitro and In Vivo

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Abstract
Altering adenovirus vector (Ad vector) targeting is an important goal for a variety of gene therapy applications and involves eliminating or reducing the normal tropism of a vector and retargeting through a distinct receptor-ligand pathway. The first step of Ad vector infection is high-affinity binding to a target cellular receptor. For the majority of adenoviruses and Ad vectors, the fiber capsid protein serves this purpose, binding to the coxsackievirus and adenovirus receptor (CAR) present on a variety of cell types. In this study we have explored a novel approach to altering Ad type 5 (Ad5) vector targeting based on serotypic differences in fiber function. The subgroup B viruses bind to an unidentified receptor that is distinct from CAR. The subgroup F viruses are the only adenoviruses that express two distinct terminal exons encoding fiber open reading frames. We have constructed chimeric fiber adenoviruses that utilize the tandem fiber arrangement of the subgroup F genome configuration. By taking advantage of serotypic differences in fiber expression, fiber shaft length, and fiber binding efficiency, we have developed a tandem fiber vector that has low binding efficiency for the known fiber binding sites, does not rely on an Ad5-based fiber, and can be grown to high titer using conventional cell lines. Importantly, when characterizing these vectors in vivo, we find the subgroup B system and our optimal tandem fiber system demonstrate reduced liver transduction by over 2 logs compared to an Ad5 fiber vector. These attributes make the tandem fiber vector a useful alternative to conventional strategies for fiber manipulation of adenovirus vectors.