Increasing degrees of plasmid vector-mediated activation of innate immune signaling pathways is an approach to improve DNA vaccine-induced adaptive immunity for infectious disease and cancer applications. potently induced type 1 IFN production in cell culture through RIG-I activation and combined high-level HA antigen expression with RNA-mediated type I IFN activation in a single plasmid vector. The eRNA Sarecycline HCl vectors induced increased HA-specific serum antibody binding avidity after naked DNA intramuscular prime and boost delivery in mice. This demonstrates that DNA vaccine potency may be augmented by the incorporation of RIG-I-activating immunostimulatory RNA into the vector backbone. Methods to increase DNA vaccine-induced innate immune responses to improve adaptive immunity are needed to enable the general application of DNA vaccination in large animals and humans. The innate immune system is present in essentially all cell types and can be directly triggered by virus- or bacterium-specific pathogen-associated molecular patterns (PAMPs). PAMPs trigger immediate antiviral or antibacterial responses, such as induction of RNA degradation, translation inhibition or cell death pathways, and secretion of stimulatory signals, such as interleukin-12 (IL-12), IL-4, and type I interferon (IFN), that activate and differentially regulate the adaptive immune response (23). A number of RNA and DNA PAMPs activate innate immunity through Toll-like receptor (TLR) signaling, for example, double-stranded RNA (dsRNA; TLR3), single-stranded RNA (ssRNA; TLR7, TLR8), and unmethylated CpG DNA (TLR9). In addition to TLRs, cytoplasmically localized B-DNA can induce interferon regulatory factor 3 (IRF-3) through IFI16-STING-TANK binding kinase 1 (TBK-1) signaling (58) and the inflammasome through activation of the AIM2 (absent in melanoma 2) receptor (reviewed in references 15 and 20) (Fig. ?(Fig.1A).1A). As well, cytoplasmic dsRNA signaling pathways, such as the recently identified retinoic acid-inducible gene I (RIG-I; ligand is a 5-PPP-containing short, blunt dsRNA) and melanoma differentiation-associated gene 5 (MDA5; ligand is a long dsRNA ) RIG-I-like helicase (RLH) pathways that activate IRF3 through interferon- promoter stimulator 1 (IPS-1; also known as MAVS, Cardif, or VISA) signaling are also critical determinants required for innate immune activation in response to viral infection (reviewed in references 21 and 23). Agonists that activate these signaling pathways have a potential application as new-generation adjuvants (26). FIG. 1. RIG-I-activating DNA vaccines. (A) Innate immune signaling in response to DNA and vector-encoded RIG-I PAMPs. Cytoplasmic (cyto) DNA may activate Sarecycline HCl Sarecycline HCl cytoplasmic receptors ZBP1 (DAI [not shown]), the IFI16 cytoplasmic receptor signaling through STING and … The RLH pathway contributes to the adjuvant activity of poly(I:C), a dual ligand for TLR3 and MDA5 (24), demonstrating that RLH agonists may have adjuvant application. Consistent with this, the TBK-1-activating N-terminal caspase recruitment site (N-CARD) of IPS-1 got adjuvant activity to boost humoral and mobile reactions to proteins vaccines (18). Oddly enough, induction of adaptive immune system reactions to influenza virus or lymphocytic choriomeningitis virus infection required TLR not RLH signaling (reviewed in reference 21). This may reflect a difference between responses that control natural infections and responses to immunization. DNA (e.g., unmethylated CpG oligonucleotide TLR9 agonist [reviewed in reference 22])- and RNA [e.g., synthetic poly(I:C) TLR3 and MDA5 agonist; ssRNA TLR7 and -8 agonists]-based adjuvants are made synthetically and are nonspecifically administered (reviewed Rabbit polyclonal to HORMAD2. in reference 4). For example, recently a bifunctional RIG-I-activating Bcl2-specific short interfering RNA (siRNA) was utilized to kill tumor cells after systemic administration (46). However, nonspecific administration of large doses of RNA and DNA may not be safe, and there is a need for molecules that can be codelivered with a DNA vaccine specifically to antigen-expressing cells. DNA PAMPs present in the vector backbone mediate the immunogenicity of plasmid vectors. For example, if a plasmid vector is delivered to the endosome (e.g., naked or liposomal plasmid delivery), unmethylated CpG motifs in the backbone stimulate innate immune signals through TLR9, resulting in improved adaptive immune responses against the transgene product. Alternatively, if plasmid is cytoplasmically delivered, B-DNA can induce innate pattern receptors through IFI16 (TBK-1 effector) or the inflammasome through AIM2 signaling. For electroporation delivery, wherein plasmid is delivered directly to the cytoplasm, TBK-1 has been implicated as a key component required for induction of adaptive humoral and cellular responses.