Investigation of novel TLR7/8 ligands in combination with TLR4 ligands as adjuvants to drive cell mediated anti-influenza immunity

Abstract

Abstract Influenza is a highly communicative viral pathogen that infects 9–35 million individuals and results in 12,000–56,000 deaths in the US annually. For the most commonly used seasonal influenza vaccine, historical efficacy rates range from 10–60% thus improvements to the current vaccine are needed. We identified a novel series of synthetic TLR7/8 ligands that improve influenza vaccine efficacy when used alone or in combination with our synthetic TLR4 ligand. In human PBMCs, TLR7/8 ligands elicited secretion of the inflammatory cytokines TNFα, IL-6, and IL-1β as well as the Th1-polarizing cytokine IL12-p70. These responses can be altered by modification of novel structural features of the TLR7/8 ligands. The addition of a synthetic TLR4 ligand modified the cytokine expression profile, indicating that the structure of a TLR7/8 ligand and/or addition of a TLR4 ligand can drive substantive changes in the innate immune response. To evaluate the adjuventicity of these TLR ligands, Balb/c mice were vaccinated with split-flu vaccine containing TLR7/8 ligands alone or in combination with our TLR4 ligand. TLR7/8 ligands increased influenza-specific total IgG and IgG2a, but not IgG1, over antigen alone. Addition of a TLR4 ligand further increased influenza-specific total IgG and IgG2a. These data demonstrate that these ligands act as adjuvants to promote a Th1 skewed humoral response. The combination of TLR7/8 and TLR4 ligands elicited superior cell mediated immunity compared to either TLR7/8 or TLR4 ligand alone. These data demonstrate that heightened innate and adaptive immune responses can be elicited through a combination adjuvant using novel synthetic TLR7/8 and TLR4 ligands.