Three separate replication-defective rAd serotype 5 vectors expressing HA (KAN-1), NP (KAN-1), and M2 (KAN-1) genes were produced as previously described [23] . Briefly, the genes were inserted into the GV11 adenoviral vector system (GenVec, Gaithersburg, MD), which is based on human serotype 5 and contains deletions of the E1 and E4 regions and part of the E3 region, rendering it replication-defective. The vectors used were as described elsewhere [23, 24] . The vector stocks were serially passaged in complementing mammalian cells (293-ORF6) to generate high-titer stocks of replication-defective adenoviruses [25, 26] . Absence of replication-competent adenovirus was confirmed by product-release assays. Gene expression in A549 (American Type Culture Collection, Manassas, VA) cells was confirmed by Western blot analysis.