Enhancing the immune responses using the synergistic effects of TLR4 and NOD2 agonists for multifaceted vaccine development

Abstract

Effective and defined adjuvanted vaccines can provide enhanced immunity to intra-cellular pathogens, which disproportionately affect certain immunocompromised individuals. Also, the importance of T-cell mediated immunity is vital in reducing the severity of intra-cellular infections. Strategies to increase vaccine immunogenicity include the addition of innovative adjuvants, which can help to achieve robust and persistent immune responses against infectious diseases. Despite the indispensable importance of adjuvants, only an extremely limited number of adjuvants have been included in licensed vaccines. That is why a search for more effective adjuvants has become one of the primary concerns in medical research. Simultaneous stimulation of germ-line encoded pattern-recognition receptors of the innate immune system, particularly Toll-like receptors (TLRs) and Nucleotide oligomerization domain (NOD)-like receptors (NLRs) can augment the cellular immune response. With this in mind, I hypothesized that adjuvants that activate TLR of NLRs would enhance vaccine response. To study this we developed a bioassay model of cytokine secretion using murine immortalized and primary antigen presenting cells(APCs), which were stimulated with diethanolamine-based lipid A (A1), a synthetic lipid A TLR4 agonist, and muramyl dipeptide (MDP),a NOD2 agonist in the presence or absence of the currently available high-dose influenza vaccine, Fluzone®. We evaluated the immune response by measuring cytokine secretion, protein cell signaling, and cell surface markers. We showed that A1 in combination with MDP was able to induce enhanced early innate immune responses synergistically by increasing ERK1/2 phosphorylation and increasing proinflammatory cytokine secretion. Next, we assessed the A1- MDP adjuvanted-Fluzone vaccine formulation against drifted influenza virus A/H3N2 variants in an antigen challenge protocol on human peripheral blood mononuclear cells (PBMCs). There were significant enhanced releases of IFNγ, IL-6, and IL-1β with no significant changes in IL-10 secretion and increased expression of CD8+ T (cytolytic T cell) cell surface markers, which suggested a polarized antigen-specific Th1 immune response. In summary, our combined adjuvant approach will ameliorate current vaccines especially for intracellular infections.