Currently, replication-deficient human adenovirus serotype 5 (AdHu5) vaccines are being evaluated against several pathogens. Several candidates have been shown to induce protective immune responses against emerging or re-emerging infectious pathogens such as Ebola and avian influenza (H5N1) viruses [4, 26, 27] Complete protection and long-term memory responses have also been reported in different animal models [7, 26, 28] ; however, the final development of AdHu5-based vector to approved human vaccines has been hampered by the presence of natural preexisting immunity to AdHu5 which is present in a large fraction of the human population. Neutralizing antibody to porcine adenovirus 3 (PAV3) was not detected from pooled immune globulin representing 10 to 60 thousand human sera suggesting that preexisting immunity to PAV3-based vaccines is not likely to be of concern for human applications. In addition, the documented compatibility of porcine and human tissues could translate into PAV3-based vaccines being efficacious while of low toxicity in humans [23] . The further development of a new adenovirus serotype also increases the spectrum of possible applications such as sequential vaccination with other adenovirus vectors (e.g. prime/boost or a second Ad-based vaccination against a different agent) [20, 29] .