113 Uncovering the dark immunopeptidome of head and neck squamous cell carcinoma (HNSCC): relevance for universal cancer vaccines, immunological monitoring and TIL therapy

Background Discoveries of the last two years have initiated a renaissance in our understanding of the targets T cells recog-nize on cancer cells. Identification of HLA-presented non-can-onical or cryptic peptides that are non-mutated and have high interpatient sharing in AML [PMID: 33740418], coupled with their absence from the thymus, led them to be designated as alternative neoantigens with potential for being universal cancer vaccines [PMID: 33852826]. These cryptic genes, in some cases, appear to play a role in promoting malignancy, further strengthening the rationale for their identification and use as targets for immunotherapy. Our group seeks to identify the Dark Immunopeptidome of HNSCC. Over the last several months we have swithed from exome-capture RNA-Seq, which fails to detect non-canonical gene sequences, to ribo-Seq, which can capture these cryptic transcripts.