Liposomes for mucosal vaccine delivery: physicochemical characterization and biological application

Abstract: Liposomes are attractive vaccine carriers due to their potential to act as adjuvants, and to the fact that their composition and characteristics are virtually endlessly customizable. However, the precise physicochemical profile of an ideal carrier liposome for mucosal vaccines is still widely unknown, and how different properties affect key steps in the acquisition of protective immunity remains to be elucidated. Additionally, there is no consensus in the field regarding characterization of vaccine formulations, often with incomplete reporting of properties as a result. The focus of this work is therefore twofold: i) to contribute to a better understanding of how the physicochemical profile of vaccine carrier liposomes impacts the development of protective immunity using models at different levels of complexity, and ii) to improve and simplify the physicochemical characterization of liposomes through development and use of new analytical methods. The work in the first area consists of, firstly, an in vivo characterization of the biological response to vaccine liposomes carrying a vaccine protein and characterized by varying surface hydrophilicity (PEGylation). This study showed that non-PEGylated vaccine liposomes more efficiently induced local cell- and antibody-mediated immune responses, as well as better protection against a lethal virus challenge than both PEGylated liposomes and free vaccine protein. Secondly, in vitro studies focused on how liposome stiffness influences dendritic cells, investigating effects on uptake, antigen presentation and cellular activation. These investigations demonstrated that stiff, gel phase liposomes were able to more efficiently activate dendritic cells and induce significantly higher levels of antigen presentation and co-stimulatory signaling compared to both soft, fluid phase liposomes, and free vaccine protein. The work in the second part comprises two studies: a surface plasmon resonance-based method to characterize the influence on liposome deformation from specific multivalent interactions with supported cell membrane mimics, and a waveguide microscopy technique for characterization of optical properties of individual liposomes. While the latter method might become valuable in the context of quantifying the efficiency of dye labelling of liposomes, the surface plasmon resonance study offered information on how liposome deformation depends on membrane stiffness and ligand-receptor pair density. Taken together, the work presented in this thesis demonstrate the value of multidisciplinary approaches to complex biological and medical challenges.