Characterization of tumor-infiltrating lymphocytes in ovarian cancer and development of a peptide-based anti-cancer vaccine

Abstract

This thesis is about the characterization of tumor-infiltrating lymphocytes (TILs) and the development of a therapeutic peptide-based anti-cancer vaccine against ovarian cancer. The thesis is divided into three parts. The first part is about tumor-infiltrating lymphocytes and their expression of co-inhibitory and co-stimulatory receptors on the cell surface. For a more precise differentiation CD8+ cytotoxic T cells were separated from CD4+ T cells and the latter were further differentiated into regulatory T cells and T-helper cells. The co-inhibitory and co-stimulatory receptors CD137, cytotoxic T lymphocyte protein (CTLA-4), lymphocyte activation gene 3 (LAG 3), programmed cell death protein 1 (PD-1) und T cell immunoglobuline (TIM-3) were analyzed separately in the three different groups of regulatory T cells, cytotoxic T cells and T-helper cells. To evaluate the expression levels of the co-receptors on tumor-infiltrating lymphocytes, they were compared to lymphocytes from the peripheral blood (PBMCs) of each patient and PBMCs from healthy donors. It was shown that most of the receptors remained absent or of low expression besides PD-1 that apparently plays a dominant role in the immunosuppressive tumor microenvironment. Besides PD-1, CD137 shows low to moderate expression across the different patients being an interesting target for immunotherapy. The second part focusses on the isolation of natural HLA ligands from ovarian tumor tissue. The eluted peptides and their respective source proteins were compared to source proteins and their peptides of benign ovarian tissue and a database that contains autopsies of different benign tissues. Through comparative profiling tumor-exclusive source proteins were determined. At the end of the thesis these naturally presented tumor-exclusive ligands were used to treat patients who have no further therapy options. The treatment was able to induce HLA class I and HLA class II mediated reactions. The reactions were monitored through the course of therapy via IFN-γ ELISpot. Overall three patients were analyzed. In the first patient treated, we were able to induce a HLA class II mediate immune response. We were able to induce an HLA class I and II mediated immune response. The third patient has shown a pre-existing immune response against one HLA class I peptide and an immune reaction was induced against three HLA class II restricted peptides.