Targeting of skin dendritic cells to improve vaccination

Dendritic cells (DC) are highly specialised cells which initiate and regulate virtually all immune reactions of the body. They do so in microbial infections, in vaccinations, but also in unfavourable immune reactions like autoimmunity or allergies. In this project we focus on the role of DC in the immunological treatment of cancer. The immune system is able to largely prevent the development of cancer. Occasionally, it leads to the regression of tumours. These observations form the basis for cancer immunotherapy that has recently seen an unprecendented upswing. Checkpoint inhibitor therapies can unleash pre-existing T lymphocytes, foremost killer cells. Clinical success is remarkable. Unfortunately, however, only less than half of the patients respond. An important reason for the therapy failures is a shortage of such pre-activated T lymphocytes upon which the checkpoint inhibitor drugs could act on. It is therefore essential to increase the numbers of such anti-cancer lymphocytes. This can be best achieved by an advancement of classical vaccination. The novelty of this project is to specifically harness the outstanding capacity of DC to generate immunity. Tumour antigens (i.e., the cancer vaccine) are targeted to the different subsets of DC in skin. This will be accomplished by fusion proteins. The cancer antigen and an antibody are joined together using molecular biology methods. These fusion proteins bind selectively to the skin DC subsets (Langerhans cells in the epidermis; DC of the dermis) and can thus deliver the antigen in a targeted fashion. This concept was discovered by Ralph Steinman, Nobel Laureate 2011. In mouse models it led to massively increased anti-cancer immunity. We will test the hypothesis that this approach will lead to massively augmented immune responses, especially of killer cells, in human skin, too. Specifically, we will investigate whether targeting Langerhans cells will yield the most powerful responses. To this end, we develop an experimental model that is as close to the clinical situation as possible. Organ cultures will be set up from skin of healthy donors. Pieces of skin will be vaccinated (injected) with the fusion antibodies. DC crawl out from these cultures and stimulate T lymphocytes of the donor. Lymphocyte functions (cell multiplication, growth factors, capacity to kill cancer cells) will be measured. Two model antigens will be used, one virus antigen and one typical cancer antigen. With three different fusion antibodies we will target the different subsets of skin DC. We aim at discovering an optimal combination of fusion antibodies and adjuvants which induce a maximal T cell (killer cell) response. We expect that our findings may contribute to a marked improvement and further development of immunotherapy of cancer, thereby complementing existing immunotherapies.

Immunotherapy of cancer has advanced tremendously in the past years, mainly due the introduction of the so-called "immune checkpoint inhibitor" therapy some 10 years ago. This therapy "unleashes" and intensifies patients' existing immunity. Yet, still today 2022, by far not all cancer patients respond favourably to this therapy. In essence, the patients' own immune response against the cancer cells is often too weak or hardly existent. In this project we explored a way to strengthen such anti-cancer immunity, in other words, to "vaccinate against cancer". Since the so-called "dendritic cells" are the crucial immune cells that can kick-off all immune responses in the body (against viruses, bacteria etc.), we attempted to deliver the cancer antigens (the cancer "vaccine") directly to these cells in the human skin, i.e., to "target" them specifically, rather than just depositing the vaccine diffusely in the skin, as it is done in conventional vaccinations. Antibodies that exclusively recognize dendritic cells served as carriers and "address labels" for the vaccine, when it was injected into the skin. We developed a skin culture model that mimicks the real life situation as close as possible. Antibody-antigen constructs were designed and produced. They were injected into these cultures and the dendritic cells, that "crawled-out" of these little pieces of skin over a period of 3 to 4 days were then tested whether they had taken up and processed the injected antigen and whether they were able to stimulate the T cells of the skin donor - T cells being those important cells that will kill the cancer cells in the body and that are therefore needed for successful cancer therapy. Indeed, we did see enhanced T cell responses in this model, partly depending on which type of skin dendritic cell was targeted within the intact skin tissue (so-called Langerhans cells of the epidermis or dermal dendritic cells). Antigen targeted to Langerhans cells in suspension, isolated from the epidermis, induced increased T cell activity as detected by an augmented production of Interferon-gamma by the T cells. With the help of a novel cell culture model that yields Langerhans cell-like cells from easily available human blood samples (as opposed to the logistically difficult work with healthy human skin samples) these findings can be studied in more detail. This model was also developed within this FWF project. It will greatly facilitate and accelerate the follow-up investigation of several parameters that will render the targeting approach more effective and ultimately feasible for clinical application. Thus, the outcome of this project represents a first and important confirmation that the concept of "antigen-targeting" is also valid for human skin, and the data obtained and published will serve as a robust basis for follow-up studies.