Positioning of the HA Globular Head within the TLR5 Agonist, Flagellin, Modulates the Immunogenicity and Reactogenicity of a Novel-H1 Pandemic Influenza Vaccine

The recent appearance of a novel H1N1 (nH1N1) virus has highlighted the importance of rapid response to emerging pandemic threats. VaxInnate has developed an influenza vaccine production system that permits rapid response on a global scale. The vaccine comprises the protective globular head subunit of HA fused covalently to the TLR 5 ligand flagellin. Using animal models that have successfully predicted the tolerated dose range in humans we have identified an optimal position for the HA globular head. Three constructs evaluated the globular head fused to the C terminus of flagellin (C-term), in place of domain 3 (R3) and in both positions (R3.2x). The three formats were tested in mouse immunogenicity and rabbit reactogenicity models. HAI assays were performed using CA/07/2009 virus. Rabbits were monitored for body temperature, food consumption and CRP. In mice, HAI titers >1:40 were achieved with 1 μg doses of all vaccines, but R3 and R3.2x vaccines yielded higher titers. In rabbits, the C-term vaccine elicited elevated temperature and CRP levels and reduced food consumption at doses well below R3 and R3.2x. Replacement of domain 3 of flagellin with the HA globular head, either R3 or R3.2x, proves safe and immunogenic in mice and rabbits. Our clinical experience with other flagellin-linked vaccines has correlated well with the rabbit model. The results predict that the R3 or R3.2x nH1 vaccines would be both safe and efficacious in humans.