OR36 Ligands distinct to ovarian cancer Hla-A*02:01

Abstract

Aim T cells recognize cancer cells via HLA/peptide complexes, and class I HLA-restricted tumor infiltrating T cells correspond to favorable prognosis in ovarian cancer, the most deadly gynecologic disease. The identification of tumor-marking HLA/peptide complexes empowers bourgeoning cancer immunotherapy strategies such as therapeutic vaccination or transgenic T cell therapy. While predictive algorithms are highly useful, a large proteomic study can both inform predictive strategies and directly identify novel cancer-associated peptides. Here, ligand elution and peptide sequencing was used to characterize ligands defining the HLA-A*02:01 of cancerous ovarian cells. Methods A secreted form of HLA-A*02:01 was stably transfected into the human ovarian cancer lines SKOV-3, A2780, OV-90 as well as the immortalized normal ovarian line FHIOSE. HLA was harvested from bioreactors of each cell line and purified by affinity chromatography. Purified peptides were fractionated by two dimensions of high-pressure liquid chromatography followed by tandem mass spectrometry and PEAKS software for peptide sequencing. Ingenuity Pathway Analysis and DAVID Bioinformatics Databases were used for source protein analysis. Results Over 30,000 peptides on average were identified at a 1% false discovery rate for each line, with peptide lengths matching expected frequencies. A clear overarching HLA-A*02:01 motif was observed, and novel length-specific motif nuances were detectable. Source protein enrichments were identified, and multiple novel as well as previously predicted peptides were found from characterized ovarian cancer antigens such as p53, human epidermal growth factor receptor 2 (HER2), mesothelin, vascular endothelial growth factor alpha (VEGFA), and epidermal growth factor receptor (EGFR). Finally, a comparative analysis between cell lines revealed consistent and defining ligands among the ovarian cancer lines. Conclusions Class I HLA gathered from tumor cells in this large-scale study provided for the direct characterization of the cancerous ligandome with unprecedented breadth. This brought to light individual peptides consistent and distinct to the HLA-A*02:01 of cancerous cells, and these ligands represent candidate peptides for use in ovarian cancer immunotherapy.