Mosaic Inverted Hemagglutinin Extracellular Vesicle Vaccines Elicit Protective Systemic and Mucosal Immunity against Heterosubtypic Influenza Infection

Developing innovative vaccine platforms and delivery strategies to induce broad, protective immunity in the respiratory tract is crucial for preventing influenza infection and transmission in potential epidemics and pandemics. In this study, we used cell-derived extracellular vesicles (EVs) as a vaccine platform to display mosaic human and avian influenza hemagglutinins (HAs) concurrently, including HA1/HA9/HA12 or HA3/HA4/HA10, on the EV surfaces. Immunization with the mosaic HA-EV vaccine elicited cross-reactive antibodies against influenza HA stalks and viruses, robust virus-specific cellular immune responses, and a balanced Th1/Th2 immune profile. Notably, the EVs demonstrated a promising application as an effective mucosal vaccine strategy, as evidenced by enhanced HA stalk- and virus-specific IgA in mucosal tissues and complete protection against heterosubtypic reassortant H7N9 and H5N1 virus infections in mice via intranasal immunization. EV-based mosaic HA vaccines hold great promise for developing universal influenza vaccines that target a mucosal route.