Synthetic lipopeptides formulated in liposomes: effect on their immune stimulatory capacity in vitro

Conjugation of antigenic peptides to lipoamino acids (LAA) has been shown to increase the membrane permeability of peptides and protects them from enzymatic degradation, but the resulting LAA-conjugated peptides were poorly soluble in both aqueous and organic solvents. To overcome the formulation issue and to further enhance the bioactivity, lipopeptide constructs (LAA-LCMV_33-41) have been encapsulated within liposomes with high entrapment efficiency. The purpose of this study was to assess the immune stimulatory capacity of these lipopeptides and their liposomal formulations. Because dendritic cells (DCs) play a key role as antigen-presenting cells in immune responses, the in vitro cellular activities of the lipopeptides and their liposomal formulations were tested by measuring the up-regulation of the surface markers CD80, CD86 and MHCII on DCs. We found that conjugation of lipoamino acid with peptide antigen enhanced its immune stimulatory capacity compared with the unmodified peptide. However, encapsulation of lipopeptides within liposomes appears to compromise their immuno-stimulatory capacity at least at a loading of 10%.