Adjuvants and Immunization Strategies to Induce Influenza Virus Hemagglutinin Stalk Antibodies

Abstract

The global population remains vulnerable in the face of the next pandemic influenza virus outbreak, and reformulated vaccinations are administered annually to manage seasonal epidemics. Therefore, development of a new generation of vaccines is needed to generate broad and persistent immunity to influenza viruses. Here, we describe three adjuvants that enhance the induction of stalk-directed antibodies against heterologous and heterosubtypic influenza viruses when administered with chimeric HA proteins. Addavax, an MF59-like nanoemulsion, poly(I:C), and an RNA hairpin derived from Sendai virus (SeV) Cantell were efficacious intramuscularly. The SeV RNA and poly(I:C) also proved to be effective respiratory mucosal adjuvants. Although the quantity and quality of antibodies induced by the adjuvants varied, immunized mice demonstrated comparable levels of protection against challenge with influenza A viruses on the basis of HA stalk reactivity. Finally, we present that intranasally, but not intramuscularly, administered chimeric HA proteins induce mucosal IgA antibodies directed at the HA stalk.

Induction of Broadly Reactive Anti-Hemagglutinin Stalk Antibodies by an H5N1 Vaccine in Humans

“…Although low levels of antibodies-and immunological memory-are associated with protection from mortality, it is questionable whether these low antibody titers have a protective effect against morbidity. Therefore, a strategy, possibly based on prime-boost regimens and/or more effective adjuvants (36)(37)(38), to induce long-term immunity may be needed for a successful stalk-based universal influenza virus vaccine. Another interesting question is how broadly reactive the antibody response induced by sequential vaccination would be.…”

Enhanced Influenza Virus-Like Particle Vaccination with a Structurally Optimized RIG-I Agonist as Adjuvant

“…We previously demonstrated that the 5=pppRNA sequence can be rationally modified to maximize the RIG-I response, leading to high expression of many proinflammatory and antiviral genes (24). Among the PRR-stimulating adjuvants, 5=pppRNA molecules, TLR agonists, defective interfering RNA produced by Sendai virus, and baculovirus-based vaccination vectors have all been utilized as adjuvants in several vaccine formulations, yielding promising data in preclinical studies (35,(43)(44)(45)(46)(47). Unfortunately, widespread implementation of PRR-based adjuvants in vaccines has been hampered by safety concerns, as infections and innate responses can sometimes be linked to autoimmune diseases (15).…”

“…To determine whether M8 possessed adjuvant activity in an in vivo model of vaccination, BALB/c mice were vaccinated by intramuscular injection with VLP coexpressing the HA and NA from H5N1 and HIV Gag protein, in combination with M8, M5, or poly(I·C) (which was previously shown to potentiate responses to influenza virus antigens [35]). Three weeks later, mouse sera were collected and analyzed for HAI activity (hemagglutination inhibition assay [HAI] or receptor blocking titers); mice immunized with VLP adjuvanted with M8, M5, or poly(I·C) displayed a 2-to 3-fold increase in HA-specific IgG titers (data not shown) and 2-to 3-fold-higher HAI antibody titers (P Ͻ 0.005) ( Fig.…”

H3 Stalk-Based Chimeric Hemagglutinin Influenza Virus Constructs Protect Mice from H7N9 Challenge

“…It is of note that DNA vaccination is not essential for induction of broad protection by cHA vaccination regimens. Vaccination with just proteins (no DNA) yielded results comparable to vaccination with DNA priming in earlier studies (18). Three weeks postprime, animals received a recombinant cH5/3 protein (H5 head derived from A/Vietnam/1203/04 on top of an H3 stalk derived from A/Perth/16/09) (16).…”