The transgene cassettes from pShuttle2-HA and pPAV227-HA-PolyA were cloned into replication-deficient DE1DE3 adenoviral vectors: pAdenoX (AdHu5, Clontech) or pFPAV227 (PAV3, VIDO, University of Saskatchewan). pAdenoX-HA was generated through digestion of both pShuttle2-HA and pAdenoX by homing endonucleases I-CeuI/PI-SceI and ligation of cohesive ends using T4 DNA ligase (Invitrogen). pFPAV227-HA was generated through homologous recombination in Escherichia coli strain BJ5183 (recBC, sbcBC) [37] of linearized pPAV227-HA-PolyA (Eco47III/TthIII1) and pFPAV227 (PacI).