Figure 1. Design and expression of H7 HA DNA vaccine inserts. (A) Schematic diagram of influenza A H7 HA gene inserts used in codon optimized DNA vaccines (A/Netherlands/219/03, H7N7), including the full-length HA antigens with natural leader sequence (H7-HA.wt) or a human tissue plasminogen activator (tPA) leader substituting the natural HA leader sequence (H7-HA.tPA) and the transmembrane/cytoplasmic region truncated HA antigens (H7-HA.dTM) with tPA leader sequence. The cleavage site between HA1 and HA2 subunits are marked. The numbers above the HA inserts denote the relevant amino acid positions in natural HA proteins. (B) western blot analysis of the expression of differently designed H7-HA DNA vaccines, including HA protein expression, secretion and susceptibility to cleavage expressed in transiently transfected 293T cell supernatant (S) and cell lysate (L).