Usefulness of adenoviral vectors derived from human adenovirus (HAd) type 5 (HAd5) is mainly limited by wide prevalence of preexisting anti-HAd5 immunity as well as non-specific tissue tropism of these vectors. As an alternative, non-human adenoviral vectors including bovine adenovirus type 3 (BAd3) are currently being investigated. Non-prevalence of BAd3 in humans and its ability to evade preexisting HAd immunity are some of the features that make BAd3 a promising vector for human gene delivery. BAd3 appears to have a tissue tropism distinct from that of HAd5 and also the repertoire of cells efficiently transduced by BAd3 is different. We performed antibody-mediated receptor blocking experiments to show that BAd3 internalization was independent of coxsackievirus-adenovirus receptor, the primary determinant of HAd5 tropism, or integrin alpha(v)beta(3), a secondary molecule involved in HAd5 entry. Using homologous and heterologous knob-mediated competition assays with recombinant knobs of HAd5, porcine adenovirus type 3 (PAd3), or BAd3, we observed that BAd3 internalization was independent of the primary receptors of HAd5 and MO. These results provide support for further exploration of BAd3 vectors for designing targeted vectors for human gene therapy. (c) 2005 Elsevier Inc. All rights reserved.