Immunotherapy of cancer with Langerin-ligand liposomes

Dendritic cells residing in the skin act as sentinels of the immune system by recognizing invading pathogens and growing tumors. They take up proteins from pathogens and tumors and after migration to the draining lymph nodes induce an immune response. These proteins, also called antigens, are cut into smaller pieces, and these peptides are presented on the surface of dendritic cells to T cells, the effector cells of the immune system. This antigen presentation process occurs in the draining lymph node and leads to the proliferation and activation of T cells. Thereafter, activated T cells infiltrate the affected skin area to destroy infected and tumor cells. This unique ability renders dendritic cells optimal targets for immunotherapy of cancer. Indeed, dendritic cell-based immunotherapy has proven its potential to prime T cell responses against tumor antigen, however clinical responses need further improvement. To arm dendritic cells for induction of tumor immunity, they need to be loaded with tumor antigens followed by strong activation so that they optimally interact with T cells. These antigens can be delivered to dendritic cells in manifold ways, such as by conjugating them to antibodies that bind to the surface of dendritic cells, which is currently tested in the clinics. Another approach involves packaging the tumor antigens in nanoparticles. Together with a research collaborator, we have developed such a delivery system to specifically target a subtype of dendritic cells in the skin, namely the Langerhans cells residing in the outermost layer of the skin, the epidermis. We will use nanoparticles coated with a ligand specific for the cell surface molecule Langerin that is uniquely expressed by Langerhans cells. These nanoparticles will ensure that encapsulated antigens are delivered to Langerhans cells for subsequent antigen presentation to T cells in draining lymph nodes. In our project, we hypothesize that antigens targeted with this specific Langerin-ligand to Langerhans cells will induce T cell responses that are able to fight melanoma, the most dangerous skin cancer type. In our project, we will investigate how Langerhans cells are optimally loaded with nanoparticles, which tumor antigens are the most efficient ones, how the T cells are optimally activated and which immunization route is the best, e.g. intradermal injection of vaccines or topical application to the skin after laser pretreatment to break the skin barrier. The overall goal of our project is to develop a novel Langerhans cell-based vaccine platform and test the efficiency of our approach for immunotherapy of melanoma.

Dendritic cells in the skin are part of the immune system and act as sentinels recognizing tumors. They engulf proteins from tumors, cut them into smaller pieces, and these peptides are presented on the surface of dendritic cells to T cells in the draining lymph nodes to induce an immune response. T cells as effector cells of the immune system infiltrate the affected skin area to destroy tumor cells. This unique capability renders dendritic cells optimal targets for immunotherapy of cancer. Indeed, adoptive transfer of dendritic cells has proven its potential to prime T cell responses against tumor antigens, however clinical responses so far are limited. Alternative therapeutic approaches aim to load dendritic cells with tumor antigens directly in the skin for induction of tumor immunity. These tumor antigens can be delivered to dendritic cells in manifold ways, e.g. by conjugation to antibodies, an approach currently in clinical testing. Tumor antigens can also be encapsulated in nanoparticles coated with specific ligands for dendritic cells. In our FWF-project we evaluated this strategy by targeting Langerhans cells in the outermost part of the skin, namely the epidermis, as this subtype of cutaneous dendritic cells can be easily reached by skin immunization approaches. As proof of principle, we used a ligand for Langerin, a molecule expressed on Langerhans cells, which was recently developed by our collaborators. Indeed, this Langerin-ligand specifically delivered antigens to Langerhans cells in the skin and induced antigen-specific T cell responses. However, we encountered difficulties with encapsulation of antigens into nanoparticles and stability issues of the nanoparticles in the skin environment. Therefore, we switched to an alternative Langerhans cell targeting vaccine platform with nucleotide-based scaffolds which are composed of modified nucleotides assembled into specific structures called either "Holliday junctions" or "Aptamers". In our study we confirmed that these scaffolds decorated with multivalent mannose sugar molecules targeted Langerin on Langerhans cells in human skin which subsequently presented scaffold-conjugated melanoma-specific peptides to CD8 T cells. Moreover, these novel vaccines can be delivered to Langerhans cells by topical application on the skin. Our findings highlight novel strategies to harness skin dendritic cells subtypes for immunotherapeutic approaches to treat melanoma. In follow-up studies we are currently evaluating the stability of these nucleotide-based scaffolds in the skin environment, their targeting potential of other skin dendritic cell subtypes in the dermal compartment of the skin and the efficiency of the T cell response to treat melanoma and other skin related diseases.