A Replicating Modified Vaccinia Tiantan Strain Expressing an Avian-Derived Influenza H5N1 Hemagglutinin Induce Broadly Neutralizing Antibodies and Cross-Clade Protective Immunity in Mice

Xiao, Haixia; Liu, Li; Zhu, Qingyu; Tan, Zhiwu; Yu, Wenbo; Tang, Xian; Zhan, Dawei; Du, Yanhua; Wang, Haibo; Liu, Di; Li, Zhixin; Yuen, Kwok-Yung; Ho, David D.; Gao, George F.; Chen, Zhiwei

To determine whether the vaccine would offer any protection, vaccinated animals were challenged with the homologous pathogenic A/BhG/QH/1/05 virus strain three weeks after the second immunization. By evaluating the body weight change and the survival rate, we found that all animals with detectable antibody responses were completely protected (Fig. 5) . Moreover, the protected mice exhibited no clinical signs of infection, including huddling, shivering and ruffled fur. In contrast, animals who received PBS and the two mice (2/5) that did not show any detectable antibody responses in the oral group, showed significant clinical signs of infection and died within 6 days post viral challenge. To determine whether or not MVTT HA-QH would confer protection against heterologous human H5N1 influenza viruses, we immunized another four groups of mice via the I.N. and I.M. routes. Here, we included the mock vaccine MVTT S for determination of whether the vaccine vector would induce any non-specific protection effects. Using the same vaccination protocol, but with a reduced dosage (1.5610 6 PFU of MVTT HA-QH ), MVTT HA-QH was able to induce both HI and NT responses, as expected (Table 3 ). In addition to the (Table 3) . Despite antigenic variation, HI and NT responses were also detected against the clade 1 A/VN/1194/ 04 ( Fig. 1 and Table 3 ). As expected, no H5-specific HI and NT responses were detected among mice immunized with MVTT S . To further determine the efficacy of MVTT HA-QH , the vaccinated animals were challenged with pathogenic A/BhG/ QH/1/05 and A/VN/1194/04 viruses 3 weeks post second immunization. Since A/HA XJ /WSN is not a pathogenic virus, it was not included in the challenge experiment. Consistent to our previous findings (Fig. 5 ), all animals with detectable antibody responses were completely protected against the homologous A/ BhG/QH/1/05 challenge (Fig. 6A) . Again, the protected mice exhibited no clinical signs of infection. Importantly, all animals with detectable antibody responses were also completely protected against the heterologous A/VN/1194/04 challenge (Fig. 6B) . In contrast, animals which received MVTT S showed significant clinical signs, including huddling, shivering, ruffled fur and body weight loss, and most of them died within 6 days post viral challenge. Despite the occurrence of clinical signs, three control animals (one in the I.M. group and two in the I.N. group) survived the A/VN/1194/04 challenge for unknown reasons (Fig. 6B) .