Fig. 2: Antibody responses to the conserved HA stalk and immuno-subdominant head domains elicited by wildtype and mHA vaccines prepared by two different methods.
Whole inactivated virus (WIV) with beta-propiolactone (BPL) and inactivated split vaccine combining BPL inactivation and Triton X-100 splitting were compared for two different vaccination strategies with WT viruses or mHA viruses. Vaccines were tested without adjuvant or with the combination with CpG 1018 (30 µg per mouse). A, B Vaccination regimen and groups. BALB/c mice (n = 10) were vaccinated in a three-dose vaccination experiment with a dose of 1 µg of HA in a 3–4-week interval. mHA inactivated split vaccines adjuvanted with AddaVax (1:1 v:v) and an unvaccinated group (PBS) were included as controls. C, D Binding of serum antibodies towards the immuno-subdominant epitopes. A cH7/BYam protein with a group 2 avian H7 head and the B/Yamagata/16/1988 HA stalk was used to measure stalk-specific antibodies in the unadjuvanted and adjuvanted groups (C). A mH11/BYam protein displaying the H11 major antigenic sites in the B/Yamagata/16/1988 HA (mH11/BYam) was used to measure antibody binding to conserved epitopes in the HA head and stalk domains in the unadjuvanted and adjuvanted groups (D). The geometric mean endpoint titer was calculated as the readout. The statistics were calculated using an unpaired one-tailed t test (*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ****P ≤ 0.0001).
