Characterising the HLA‐I immunopeptidome of plasma‐derived extracellular vesicles in patients with melanoma

Extracellular vesicles (EVs) frequently express human leukocyte antigen class I (HLA‐I) molecules. The immunopeptidomes presented on EV HLA‐I are being mapped to provide key information on both specific cancer‐related peptides, and for larger immunopeptidomic signatures associated with disease. Utilizing HLA‐I immunoisolation and mass spectrometry, we characterised the HLA‐I immunopeptidome of EVs derived from the melanoma cancer cell line, ESTDAB‐026, and the plasma of 12 patients diagnosed with advanced stage melanoma, alongside 11 healthy controls. The EV HLA‐I immunopeptidome derived from melanoma cells features T cell epitopes with known immunogenicity and peptides derived from known tumour associated antigens (TAAs). Both T cell epitopes with known immunogenicity and peptides derived from known TAAs were also identifiable in the melanoma patient samples. Patient stratification into two distinct groups with varying immunological profiles was also observed. The data obtained in this study suggests for the first time that the HLA‐I immunopeptidome of EVs derived from blood may aid in the detection of important diagnostic or prognostic biomarkers and also provide new immunotherapy targets.