Enhanced antigen delivery via cell death induced by the vaccine adjuvants

The objective of this study was to examine the effect of cell death induced by the emulsion adjuvants on the in vitro delivery of antigens into the antigen-presenting cells (APCs). J774A.1 murine macrophage-like cells, serving as the APCs, were pulsed with various vaccine adjuvants, and incubated with fluorescein isothiocyanate-conjugated bovine serum albumin (BSA-FITC), with or without adjuvants-pretreated EL4 murine thymoma cells, followed by analysis by flow cytometry and fluorescence microscopy. To assess the potential oxidative burst in the macrophages after adjuvant treatment, cells were probed with 2′,7′-dichlorofluorescein diacetate (DCFH-DA) and hydroethidine (HE), and analyzed by flow cytometry. Treatment of macrophages with the emulsion adjuvants, followed by co-incubation with the adjuvant-induced dead EL4 cells, resulted in a substantial uptake of soluble antigens into the APCs and generation of a considerable amount of reactive oxygen species (ROS), including hydrogen peroxide and superoxide. Pre-treatment of J774A.1 cells with several endocytosis inhibitors, including amiloride, brefeldin A or cytochalasin B, on the other hand, reduced internalization of soluble antigens. It was concluded that co-treatment of macrophages with the emulsion adjuvants and the adjuvant-induced dead cells facilitated delivery of soluble antigens, via both phagocytosis and macropinocytosis, into the antigen-presenting cells.