Enhanced in vivo immunity and protection provided by cationic lipid-DNA complex adjuvanted influenza vaccination is independent of Toll-like receptor 9 (106.16)

Abstract

Abstract As current licensed influenza vaccines provide little or no cross-protective immunity, we have pursued using cationic lipid-DNA complex (CLDC) adjuvant to boost adaptive immunity to inactivated influenza vaccines. CLDC consists of a non-coding plasmid DNA, rich in immunostimulatory CpG motifs, which is encapsulated in cationic lipids. Previous murine and non-human primate studies showed that CLDC adjuvanted influenza vaccination induced more robust immunity and cross-protection. We hypothesized that the CLDC plasmid mediates these effects, at least in part, in a TLR9-dependent manner. Bone-marrow derived dendritic cells (BMDCs) incubated in vitro with CLDC secreted high levels of interferon-alpha (IFN-α), and this induction required CLDC’s DNA component. CLDC-induced IFN-α expression was significantly reduced using TLR9-/- BMDCs. We next vaccinated wildtype and TLR9-/- mice with CLDC-adjuvanted inactivated influenza vaccines. Surprisingly, CLDC’s immunostimulatory responses in vivo were TLR9-independent in that there was no significant difference between wildtype and knockouts for either vaccine immunogenicity (influenza-specific antibody and T-cell responses) or for cross-protection after viral challenge. These studies suggest that the DNA moiety of CLDC enhances immune responses in vivo by a novel, TLR9-independent mechanism. Determining this mechanism will likely be important in the optimal application of CLDC as an adjuvant to human vaccination.