Mucosal Vaccine Development Based on Liposome Technology

Figure 3

Various properties of liposome-based vaccines. (a) The effect of altered surface charge on liposome function has been extensively examined [32, 33]. (b) The lipid composition is critically influencing the immune response [34]. (c) Also the localization of the antigen on or inside the liposome plays an important role in shaping the immune response to the vaccine. There are several modes of antigen association to liposomes. Firstly, antigens may be encapsulated in the aqueous core or they could be linked to the surface via covalent attachment. Alternatively, a hydrophobic anchor can be used to attach the antigen to the surface via adsorption or through electrostatic interactions with lipids of opposite charge. For proteins with a hydrophobic region one may even successfully insert these in the liposome membrane. The liposome may also be used as an immunoenhancer simply by admixing the antigen and the liposomes. (d) Only few studies have addressed the impact of size or lamellarity [35, 36]. (e) Modifications of liposomes to increase their immunoenhancing effect can be done through attaching PAMPs, such as lipid A (LPS), or through specific targeting strategies using cell-specific antibodies (anti-CD103 or -DEC205) [16, 37]. (f) Other modifications, including addition of poly(ethylene glycol) (PEG) or different polymer coatings that increase the liposome penetration of the mucosal barrier or to increase liposome resistance in biological fluids, have also been developed [38].