Self-amplifying mRNA expressing COBRA hemagglutinin elicits long-lasting, broadly reactive antibodies against seasonal influenza A viruses

Development of universal or broadly-reactive influenza virus vaccines is critical for addressing emerging pandemic strains, as well as improving the effectiveness and longevity of annual, seasonal influenza virus vaccines. The next generation of influenza vaccines need to address expanding the breadth of vaccine induced immune response to neutralize drifted variants, enhance the longevity of elicited immunity, and preferably use single-shot platforms that will reduce the number of vaccinations and expand the number of doses available. In this report, influenza hemagglutinin sequences, developed using computationally optimized broadly-reactive antigen (COBRA) methodology, were expressed from a self-amplifying mRNA (samRNA) vector to elicit broadly-reactive, protective immunity following a single vaccination of mice or ferrets. Three COBRA HA antigens representing an H1 HA (Y2) or two H3 HA (J4 or NG2) were expressed from individual samRNA vectors and administered individually or mixed as H1/H3 HA samRNA vaccines. In addition, two HA antigens were expressed from the same vector (Y2-J4 or Y2-NG2) as a dual expressing samRNA vaccine. Mice or ferrets vaccinated with these samRNA vaccines had long-lasting antibodies with hemagglutination-inhibition activity against a panel of H1N1 and H3N2 influenza strains representing past, current, and future drifted influenza virus variants. In addition, samRNA expressed COBRA HA antigens elicited H1 and H3 specific T cell resposnes against HA head and stem regions. Animals challenged with H1N1 or H3N2 influenza viruses had little weight loss or signs of morbidity and little to no virus detected in the lungs or nasal washes following challenge. Overall, samRNA vectors, expressing COBRA HA antigens, efficiency elicited broadly-reactive and protective immune responses following a single vaccination.