We evaluated different DNA immunogens [HA (KAN-1) alone; HA (KAN-1) with NP (PR/8); HA (KAN-1) with NP (PR/8) and M2 (KAN-1); or NP (PR/8)] for their ability to elicit protective immunity against A/Vietnam/1203/2004 (H5N1) using the mouse challenge model. Study cohorts consisted of 10 female BALB/c mice for the HA alone, HA+NP, and HA+NP+M2 groups, and 5 animals for the NP alone and vector control groups. Serum was collected 10 days after the last DNA vaccination, and end-point ELISA titers were evaluated after DNA immunization ( Figure 2 ). All HA-containing groups showed an increase in HA ELISA titer compared to the control cohort (p,0.0013) (Figure 2 , left panel). As might be expected, these levels appeared to decrease with the number of gene products in the DNA vaccine, although significant differences were not observed amongst the HAcontaining groups.