TLR2/TLR7 Conjugated Adjuvant Enhances Anti-Nucleoprotein Immunity and Provides Protection Against Lethal H1N1 Influenza Infection 2253752

Introduction Influenza A virus (IAV) poses a significant public health threat due to its high mutation rate. Antigenic drift (slight changes in the outer coat proteins) leads to seasonal epidemics, while antigenic shift (new hemagglutinin (HA) or neuraminidase (NA) antigens) can produce novel strains with pandemic potential. Limited population immunity to these new strains increases the risk of severe illness and mortality, underscoring the urgent need for a universal vaccine. Methods To develop a universal influenza A virus (IAV) vaccine that induces robust B and T cell memory responses we take a two-layered approach. First, we utilize toll-like receptor (TLR) agonists as vaccine adjuvants and second, we add a conserved internal protein (nucleoprotein (NP)) to increase the breadth of the immune response and activate T cell responses to provide a second armament of protection. Results We show that a conjugated, dual TLR2/7 agonist CL413 and NP antigen can enhance both antibody and T cell responses after intramuscular (i.m.) injection and provide enhanced heterosubtypic immunity to lethal IAV infection compared to either agonist alone. In determining the utility of this approach across mouse strains we found that BALB/c mice generated a hyperinflammatory response to the initial i.m. vaccination with CL413 and antigen, with the TLR2 agonist being responsible for the higher side effects. In contrast, the i.m. injection of CL413 (or TLR agonist) in C57BL/6 strain showed no adverse outcomes. Interestingly, vaccination of BALB/c mice via the intranasal (i.n.) route did not induce visible side effects, yet provided complete protection against challenge. Conclusion Together, these data indicate that conjugated adjuvants with conserved IAV proteins provide superior heterosubtypic protection compared to antigen alone, or antigen with singular agonists. Investigating the protective mechanisms of this combination strategy, brings us closer to developing a universal vaccine against both seasonal and pandemic IAV strains.