Plasmids encoding HA (A/Thailand/1(KAN-1)/2004, Gen-Bank AY555150), NP (A/Thailand/1(KAN-1)/2004, GenBank AAV35112 and A/PR/8/34, GenBank AAM75159), and M2 (A/Thailand/1(KAN-1)/2004, GenBank AAV35111) were synthesized using human-preferred codons and constructed in a CMV/R backbone by GeneArt (Regensburg, Germany) as previously described [22] . Gene expression was confirmed using 293T (Invitrogen, Carlsbad, CA) transfected cells by Western blot analysis.