We have generated candidate vaccines against H9N2, H5N1, H7N3, H2N2, H6N1, H2N3, H7N7 and H7N9 influenza viruses. Based on promising preclinical data in mice and ferrets, clinical lots of these vaccines were generated for Phase I clinical trials of the safety and immunogenicity of the vaccines for healthy adults under an IND. The findings from the H9N2, H5N1, H7N3, H6N1 and H2N2 vaccine studies were included in previous reports. A novel reassortant avian H7N9 virus crossed the species barrier and caused a zoonotic outbreak in China in 2013 and reemerged in 2014 and 2015 in a seasonal pattern, causing significant morbidity and mortality in humans. Because of its continued circulation in poultry and the large number of sporadic human infections, H7N9 viruses pose a pandemic threat. Therefore, we developed a live-attenuated A/Anhui/1/2013 (H7N9) virus vaccine and evaluated it in seronegative heathy younger and older adults. We assessed the ability of one or two doses of the vaccine to induce immune memory. Healthy subjects in two age groups (18-49 and 50-70 years old) with undetectable hemagglutination-inhibiting (HAI) antibody to H7N9 were enrolled. Younger subjects received either one or two intranasal doses of the vaccine, while older subjects received a single dose. All subjects received a single intramuscular dose of 30 micrograms of unadjuvanted, antigenically matched A/Shanghai2/2013 (H7N9) pandemic inactivated influenza vaccine (pIIV) 12 weeks after their last dose of pLAIV. Both the H7N9 pLAIV and pIIV were well tolerated. Serum HAI antibody responses were detected in 1/49 subjects after one dose, and in 2/16 younger subjects after a second dose of pLAIV. Subsequently, strong serum antibody responses were detected after a single dose of pIIV in all groups with induction of antibody-dependent cellular cyotoxicity (ADCC) as well as of HAI and neutralizing activity that was broadly reactive against H7 viruses including a more recent H7N9 isolate. We conclude that the H7N9 pLAIV candidate was safe in both younger and older age groups. Priming with pLAIV resulted in responses to subsequent pIIV that exceeded those seen in naive subjects in previous reports and were more frequent than those reported after two doses of pIIV. The H7N9 pLAIV induced strong immune memory in both younger and older subjects that could be demonstrated by exposure to subsequent antigenic challenge. The hemagglutinin (HA) protein is the main target of vaccine-induced neutralizing antibodies but little is known about the H7 HAs antigenic sites or the in vitro activity of human monoclonal antibodies generated following H7N9 vaccination. In collaboration with Patrick Wilson at the University of Chicago, we generated monoclonal antibodies from healthy individuals who received the candidate influenza A/Anhui/1/2013 (H7N9) vaccine. We characterized twelve H7-reactive monoclonal antibodies that were grouped into three classes based on hemagglutination inhibition activity (HAI) and neutralization activity. We mapped the H7 HA antigenic sites by generating escape mutants and identified previously unknown epitopes on the head and stalk domains. We also identified a novel class of protective human monoclonal antibodies that are broadly cross-reactive in ELISA assays but do not display neutralization activity in vitro. These antibodies recruit effector cells via their Fc region as a mechanism of protection. Importantly, all three classes of antibodies protect mice in vivo during challenge passive transfer experiments. Taken together our findings reveal previously uncharacterized properties of vaccine-induced antibodies and overall contribute to a better understanding of the human monoclonal antibody response to influenza in the context of new vaccine strategies.
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