Antigen delivery for cross priming via the emulsion vaccine adjuvants

The function of emulsion adjuvants in vaccine antigen delivery remains unclear. To investigate the roles of emulsion adjuvants in cross presentation of exogenous antigens, a series of emulsions were prepared for both in vitro and in vivo studies. Bone marrow-derived dendritic cells (BMDCs) were treated with the adjuvants and analyzed by flow cytometry for the expression of costimulatory molecules. The activation of antigen-specific T cells in vitro was determined with B3Z cells. Antibody secretion in the draining lymph nodes of emulsion adjuvant-treated animals was measured by enzyme-linked immuno-spot (ELISPOT) assays, and antigen-specific proliferation of cells was conducted to examine the roles of emulsion adjuvants in antigen delivery. Data on phagocytosis of adjuvant-treated cells correlated well with the degree of cell death induced by the emulsion adjuvants. Significant inflammatory infiltration and cell death were observed in vivo at the adjuvant injection sites, as demonstrated by hematoxylin and eosin (H&E) staining and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays. Ovalbumin (OVA)-based ELISPOT assays showed that L121-adjuvant, containing Pluronic L121, induced the most significant cell death also stimulated the strongest antibody-producing response in the draining lymph nodes, consistent with the data on the proliferation of antigen-specific T cells and activation of B3Z cells in vitro. Results presented in this study have demonstrated the roles of emulsion adjuvants in induction of cell death and delivery of exogenous antigens for cross-priming, leading to stimulation of antigen-specific immune responses.