Combination of STING and TLR 7/8 Agonists as Vaccine Adjuvants for Cancer Immunotherapy

SIMPLE SUMMARY: The clinical use of immunoadjuvants is limited by transient responses and various side effects. This study investigated the multi-adjuvant approach of combining a TLR 7/8 agonist (522) and a STING agonist (DMXAA) to generate a robust anticancer immune response. Immunization with ovalbumin+DMXAA+522 resulted in the activation of DCs in lymph nodes, spleen, and tumor. The combination also elicited stronger antigen-specific CD8+ T cell and NK cell responses than the control or individual treatments. Immunization with OVA+DMXAA+522 resulted in significant tumor growth inhibition and improved survival compared to other controls. ABSTRACT: Immunostimulatory adjuvants that potently activate antigen-presenting cells and (in turn) prime cytotoxic T cells are a key component of anticancer vaccines. In this study, we investigated a multi-adjuvant approach combining a TLR 7/8 agonist (522) and a STING agonist (DMXAA) to promote enhanced antigen cross-presentation, stimulate specific antitumor T-cell responses, and provide improved anticancer efficacy. In vitro experiments using bone marrow-derived dendritic cells (BMDCs) confirmed enhanced activation with the 522-DMXAA combination based on both co-stimulatory molecule expression and pro-inflammatory cytokine secretion. The immunization of mice with vaccines comprising both 522 and DMXAA resulted in greater antitumor efficacy in B16F10 melanoma and MB49 bladder tumor models relative to mono-agonist vaccines. Flow cytometry-based analysis of immune cells from immunized mice revealed the significant activation of antigen-presenting cells, increased numbers of activated and Ag-specific CD8+ T cells in the spleen and lymph nodes, modest NK cell activation, and an overall reduction in CD206(+) macrophages. These results were supported by an increase in the levels of IFN-γ and a reduction in IL-10 levels in the sera. Taken together, these findings demonstrate the potential of the TLR7/8 and STING agonist combination as vaccine adjuvants to activate both innate and adaptive immune responses.