Targeting antigen presenting cells with lipid-based vaccines for the induction of strong immune responses

Our immune system is essential for the protection against and destruction of pathogens, but also has an important role in cancer and tumor control. Therapy that is committed to use the immune system as anti-cancer strategy is called immunotherapy. Effective immunotherapy depends on the induction and activation of both innate (non-specific) and adaptive (specific and memory) immunity simultaneously combined with inhibition of tumor induced immune suppression. Vaccination, widely applied in the field of virology, can also be exploited in cancer to provide activation signals to the innate and adaptive immune players. Central players of innate and adaptive immunity that need to be instructed by vaccines are antigen presenting cells (APCs) such as dendritic cells (DCs) or Langerhans cells, which are both located in the skin, the prime vaccination site. APCs can be seen as messengers of the immune system that take up antigens, either tumor or pathogen derived, process and present them to T-cells that belong to the adaptive immunity and create specifity and memory. Stimulation of APCs facilitates their migration to lymph nodes where they can establish activation of innate immune cells, such as invariant natural killer T-cells (iNKT) in addition to activation of the adaptive immune response trough cross-presentation of antigens to CD8+ and CD4+ T-cells. These CD8+ and CD4+ T-cells can be respectively seen as effector cells that can kill tumor cells and helper cells that support CD8+ T-cells. iNKT can be described as immune boosters that aid in activation of both CD8+ and CD4+ T-cells, but also DCs and natural killer cells (which can kill tumor cells) but above all iNKT also exert killing capacities themselves. Since APCs play such a central role in the activation of antigen specific T-cell responses and iNKT, it is an attractive strategy to develop vaccines that are specifically delivered to APCs. These APCs targeting vaccines can consist of different components, that next to activation of antigen specific T-cells, can lead to iNKT activation. An example of such component is the sponge derived glycolipid alpha-galactosyl ceramide (αGC) that once presented by DCs can activate iNKT. Because APCs express a wide variety of receptors, these immune cells can be easily targeted via use of their specific ligands. Previous work has already proven the efficacy of glycans as targeting moieties to C-type lectin receptors on DCs, an example of such a glycan is Lewis Y (LeY). The aim of the work presented in this thesis was to develop lipid-based vaccines that specifically target APCs to activate both players of the innate and adaptive immune system. Different targeting moieties were tested and include palmitic acid (Chapter 2), LeY glycan (Chapter 3,4), ganglioside GM3 (Chapter 5) and immature mannose sugar structures (Chapter 6). These moieties targeted lipid bilayers (palmitic acid), DC-SIGN receptor (LeY, mannose) and CD169 (GM3) on APCs. Additionally in some of the studies the inclusion of αGC in APC targeting vaccines was investigated (Chapter 3,4,5). Targeting vaccines to APCs could increase antigen specific immune responses (Chapter 2,3,5,6) and iNKT activation (Chapter 3). Interestingly, we could also demonstrate the additive value of iNKT activation on CD8+ T-cells trough targeting of CD169+ macrophages with GM3-αGC containing liposomes (Chapter 5). We additionally demonstrated that increased CD8+ T-cell responses induced by palmitoylated antigens resulted in enhanced tumor control in vivo (Chapter 2), while on the opposite, decreased antigen specific T-cell induction with LeY-αGC liposomes did not lead to diminished tumor control (Chapter 4). In conclusion, our studies show the ample possibilities of formulating vaccine modalities using lipid based components for efficient APC targeting and demonstrate that APC targeting can result in effective immune activation and anti-tumor immunity.