Combination of dmLT and MPL-A adjuvants synergistically and differentially activates the canonical inflammasome in DCs and macrophages in the absence of pyroptosis

Abstract

Abstract The initiation of innate immune responses is critical for the formation of a protective adaptive immune response following vaccination. Innate immune cells, such as dendritic cells (DCs) and macrophages, phagocytose and display antigen, produce immune modulators and migrate to lymphoid tissues, leading to the activation of naïve T cells. These professional antigen-presenting cells are activated in response to pathogen or danger associated molecular patterns, a process that is normally not robust with vaccine antigen alone. Adjuvants are able to increase the immunogenicity of vaccine antigens by influencing the activation status of these innate immune cells. Only a few vaccine adjuvants are currently approved for use in the US and, along with the discovery of novel adjuvants, combination adjuvants are likely to have a major impact on future vaccine development. Here, we investigated the ability of both the double mutant Escherichia coli heat labile toxin (dmLT) and the TLR4 agonist monophosphoryl lipid A (MPL-A) to drive innate and adaptative immune responses independently and in combination. We found that the combination adjuvant induces more robust activation of DCs and macrophages than either adjuvant alone, leading to the formation of the NLRP3 inflammasome complex and GSDMD independent secretion of IL-1b in the absence of pyroptosis. Furthermore, RNA sequencing and ingenuity pathway analysis support that the combination adjuvant may allow these DCs to polarize a multi-faceted Th1/2/17 CD4 T cell response. Because macrophages and DCs have distinct roles in the interface between innate and adaptive immunity, understanding the cellular and molecular actions of adjuvants on these cells is critical when developing new vaccines.