ITOC2 – 021. The melanoma immune-peptidome for T-cell-based anti-tumour immunotherapies

Metastatic malignant melanoma (MMM) is a highly aggressive disease. Immune checkpoint inhibitors have proved immunotherapeutic efficacy; however, not all patients profit and severe side effects may occur. Currently, little is known about the tumour-specific targets and the tumour-reactive effector cells that are involved. Aiming to characterise the melanoma immune-peptidome, we purified HLA-I and HLA-II complexes from MMM patient tumours and accurately identified thousands of unique HLA binding peptides per tissue sample, using state-of-the-art mass spectrometry. We applied algorithms for database search in combination with de-novo sequencing and identified many novel cancer-associated peptides from known melanoma-specific antigens (PRAME, Tyrosinase, MAGEA3, PMEL, CTAG1A, PAX3 etc.). We further extended our search to post-translationally modified peptides that potentially serve as neo-antigens. After in vitro T-cell stimulation assays, we detected elevated levels of peptide-specific T-cells that displayed functional responses against peptide-pulsed target cells as well as tumour reactivity. We established this large-scale resource of the melanoma in vivo presented immune-peptidome that contains many novel targets validated by immune reactivity. These data provide the fundament for further optimisation of treatment modalities for this life-threatening disease.