Overcoming tolerance to tumour-antigens using molecularly informed epitope-modification to expand restructured oligoclonal CD4+ T-cell responses

Robust anti-tumour helper CD4⁺ T cell (T_H1) responses can lead to control of cancers. However, the effectiveness of therapeutic vaccines to shared tumour associated antigens has often disappointed, reflecting a degree of immunological tolerance to germ-line encoded antigens. Bespoke modifications to HLA class II-presented epitopes, targeting the non-core bound peptide flanking residues (PFRs) can transform T_H1 responses. We identified two HLA-DR4 (DRA1^*0101,DRB1^*0401)-restricted epitopes derived from a cancer-testis antigen DNAJB7, expressed by many epithelial cancers. HLA-peptide binding assays ranked these immunodominant epitopes as surprisingly weak binders (IC50<10,000 nM). Introduction of bespoke amino acid substitutions to the PFRs impacted on αβ T cell receptor usage reflected by altered clonal selection. Specific T_H1 responses were unmasked and/or expanded in 12/20 (60%) HLA-DR4+ donors – half of whom demonstrated null responses to wild type peptides – increasing the magnitude of IFN-γ+ T cells in cancer patients (p<0.001). PFR-modification generating “pseudo-neoantigens” overcomes immunological tolerance providing a novel avenue for improved tumour vaccines.