ABSTRACT
Many immunostimulants act as vaccine adjuvants via activation of the innate immune system, although in many cases it is unclear which specific molecules contribute to the stimulatory activity. QS-21 is a defined, highly purified, and soluble saponin adjuvant currently used in licensed and exploratory vaccines, including vaccines against malaria, cancer, and HIV-1. However, little is known about the mechanisms of cellular activation induced by QS-21. We observed QS-21 to elicit caspase-1-dependent IL-1ß and IL-18 release in antigen-presenting cells such as macrophages and dendritic cells when co-stimulated with the TLR4-agonist adjuvant monophosphoryl lipid A. Furthermore, our data suggest that the ASC-NLRP3 inflammasome is responsible for QS-21-induced IL-1ß/IL-18 release. At higher concentrations, QS-21 induced macrophage and dendritic cell death in a caspase-1-, ASC-, and NLRP3-independent manner, whereas the presence of cholesterol rescued cell viability. A nanoparticulate adjuvant that contains QS-21 as part of a heterogeneous mixture of saponins also induced IL-1ß in an NLRP3-dependent manner. Interestingly, despite the role NLRP3 plays for cellular activation in vitro, NLRP3-deficient mice immunized with HIV-1 gp120 and QS-21 showed significantly higher levels of Th1 and Th2 antigen-specific T cell responses and increased IgG1 and IgG2c compared with wild type controls. Thus, we have identified QS-21 as a nonparticulate single molecular saponin that activates the NLRP3 inflammasome, but this signaling pathway may contribute to decreased antigen-specific responses in vivo.
Subject(s)
Adjuvants, Immunologic/pharmacology , Carrier Proteins/metabolism , Dendritic Cells/drug effects , Immunity, Innate/drug effects , Inflammasomes/drug effects , Macrophages/drug effects , Saponins/pharmacology , AIDS Vaccines/agonists , AIDS Vaccines/immunology , Adjuvants, Immunologic/analysis , Adjuvants, Immunologic/chemistry , Animals , Bone Marrow Cells/cytology , Bone Marrow Cells/drug effects , Bone Marrow Cells/immunology , Carrier Proteins/genetics , Cell Survival/drug effects , Cells, Cultured , Dendritic Cells/cytology , Dendritic Cells/immunology , GTP-Binding Proteins/genetics , GTP-Binding Proteins/metabolism , HIV Envelope Protein gp120/agonists , HIV Envelope Protein gp120/immunology , Immunoglobulin G/analysis , Immunoglobulin G/biosynthesis , Inflammasomes/immunology , Inflammasomes/metabolism , Lipid A/agonists , Lipid A/analogs & derivatives , Lipid A/pharmacology , Macrophages/cytology , Macrophages/immunology , Mice, Inbred C57BL , Mice, Knockout , NLR Family, Pyrin Domain-Containing 3 Protein , Saponins/analysis , Saponins/chemistry , Solubility , Th1 Cells/drug effects , Th1 Cells/immunology , Th1 Cells/metabolism , Th2 Cells/drug effects , Th2 Cells/immunology , Th2 Cells/metabolismABSTRACT
Immunogenic properties of the combined vaccine CombiHIVvac, comprising polyepitope HIV-1 immunogens, one being the artificial polyepitope protein TBI, containing the T- and B-cell epitopes from Env and Gag proteins, and the DNA vaccine construct pcDNA-TCI coding for the artificial protein TCI, carrying over 80 T-cell epitopes (both CD4+ CTL and CD8+ Th) from Env, Gag, Pol, and Nef proteins, are studied in this work. The data reported demonstrate clearly that a combination of two B- and T-cell immunogens (TBI and TCI) in one construct results in a synergistic increase in the antibody response to both TBI protein and the proteins from HIV-1 lysate. The level of antibodies induced by immunization with the constructs containing either immunogen alone (TBI protein or the plasmid pcDNA-TCI) was significantly lower as compared to that induced by the combined vaccine. The analysis performed suggests that the presence of CD4+ T-helper epitopes, which can be presented by MHC class II, in the protein TCI may be the main reason underlying the increased synthesis of antibodies to TBI protein due to a CD4-mediated stimulation of B-cell proliferation and differentiation.