Effective stimulation of invariant natural killer T cells by oligomannose-coated liposomes

vThe in vitro and in vivo response of invariant natural killer T (iNKT) cells to alpha-galactosylceramide (αGC)-containing oligomannose-coated liposomes (αGC-OMLs) was examined to determine whether selective delivery of αGC to dendritic cells (DCs) and subsequent activation of iNKT cells could be achieved. Splenocytes stimulated with αGC-OMLs produced higher levels of IFN-γ compared to those stimulated with bare liposomes without an oligomannose coating (αGC-BLs). The ratio of IFN-γ/IL-4 produced from αGC-OML-treated splenocytes was higher than those produced from αGC-BL- and soluble αGC-treated cells. Depletion of CD3(+)-, DX5(+)- or CD11c(+)-cells from splenocytes almost completely abolished the αGC-OML-stimulated cytokine production, suggesting that both NKT cells and DCs were involved in the response to αGC-OML stimulation. In addition, αGC-OMLs were incorporated into both splenic and bone marrow-derived DCs more effectively than αGC-BLs. iNKT cells stimulated with DCs with ingested αGC-OMLs produced much higher levels of IFN-γ than those stimulated with DCs containing αGC-BLs or soluble αGC. Systemic administration of αGC-OMLs led to modification of the kinetics of IFN-γ production in vivo and also resulted in predominant production of IFN-γ from splenocytes over IL-4. In addition, iNKT cells proliferated and expanded upon in vivo activation of the cells with αGC-OMLs much more extensively than with αGC-BLs or soluble αGC. Collectively, our results suggest that αGC-OMLs can be used as a preferential delivery system for lipid antigens to DCs to activate iNKT cells in vivo and ex vivo.