FIG 4.
CA4-DelNS1 as a master backbone for construction of DelNS1 H3N2 LAIV. (A) Generation of CA4-DelNS1-HK4801 (H3N2) by plasmid transfection. CA4-DelNS1-HK4801 (H3N2) virus was rescued with HA and NA plasmids derived from the A/Hong Kong/4801/2014 (H3N2) strain and 6 internal gene plasmids from the CA4-DelNS1 virus containing adaptive mutations, as described for Fig. 1. (B) CA4-DelNS1-HK4801 cannot replicate in IFN-competent A549 cells. (C) CA4-DelNS1-HK4801 replication efficiency varied with temperature in MDCK cells. (D) CA4-DelNS1-HK68 (H3N2) protects mice from challenge with homologous HK68-MA virus. Mice were vaccinated with CA4-DelNS1-HK68 (HK68-WT) virus (2 × 106 PFU) or PBS and after 3 weeks were challenged with HK68-MA (mouse-adapted) virus. (E) CA4-DelNS1-HK4801 protects mice from challenge with heterologous HK68-MA virus. Mice were vaccinated with CA4-DelNS1-HK4801 (H3N2) virus (3 × 107 PFU) or PBS and were challenged later with HK68-MA virus. Body weight and survival were observed for 14 days. Body weight data represent mean values ± standard deviations of results from 6/7 mice. Statistical comparisons between means were performed by Student's t test. ***, P < 0.001; **, P < 0.01; *, P < 0.05.