Project Summary/Abstract
The burden of influenza remains high, with seasonal epidemics resulting in 3-5 million cases of severe illness
globally and ~650,000 fatalities/year. While immunity to influenza virus acquired through natural infection is
relatively broad and long-lived, immune responses induced through vaccination with current vaccines are short-
lived and narrow, requiring annual reformulation and revaccination. It is unclear what causes such dissimilarities
between infection- and vaccine-induced immunity, however major differences include route of exposure
(respiratory vs. parenteral), antigen type (live vs. inactivated virus/protein), and the robust activation of viral-
specific innate immune responses during infection. Current influenza vaccines elicit immune responses primarily
directed towards epitopes in the highly variable immunodominant head domain of the viral hemagglutinin (HA).
While antibodies directed towards the more conserved HA stalk domain provide cross-strain protection, this
domain is poorly immunogenic. HA head dominance compounded with the rapid pace of antigenic drift severely
limits cross-protection. Broad-based cellular immunity and mucosal immunity are also key to heterosubtypic
protection, however current parenteral vaccines do not induce these sufficiently. Thus, development of more
effective adjuvants and vaccination strategies targeting the mucosal route are clearly needed. Natural infection
with influenza virus stimulates strong adaptive immune responses through activation of Toll-, RIG-I-, and NOD-
like receptors (TLRs, RLRs, NLRs). As induction of appropriate innate responses is crucial for long-lasting
adaptive immunity and for shaping the correct types of immune responses, we will employ a rationally designed
intranasal combination adjuvant to activate all three pathways through the mucosal route to more closely mimic
natural infection, which we hypothesize will lead to more robust and durable vaccine responses. This adjuvant
consists of a nanoemulsion adjuvant (NE) that activates TLRs and NLRP3 and an RNA agonist of RIG-I derived
from the defective interfering RNA of Sendai virus (IVT). NE/IVT induces synergistic immune responses against
a variety of viral antigens, with magnified TH1-biased cellular immunity and mucosal immune responses. Here,
we will compare this adjuvant to two adjuvants licensed for parenteral vaccination with influenza vaccines (AS03
and MF59) to improve immune responses to two different antigen systems that have broadened heterosubtypic
protection in preclinical and clinical settings: (1) a sequential regimen utilizing split viruses containing chimeric
HAs with different “exotic” avian HA head domains all with the same stalk domain to guide immune responses
to epitopes in the stalk, and (2) a recombinant tetrameric neuraminidase. Human immune responses to influenza
vaccines are heavily influenced by pre-existing immunity acquired through past infections and/or immunizations.
We will further determine whether the immune responses driven by mucosal administration of NE/IVT with these
antigen systems can better take advantage of such pre-existing immune responses compared to parenteral
vaccination with AS03 by redirecting memory responses to more conserved epitopes.
