P09

Targeting a shared neoepitope derived from non-canonical translation of c-Myc oncogene in cancer cells

E Baulu(1) A Bolon(1) E Etchegaray(2) O Tabone(2) F Raimundo(1) A Merienne(3) J Martin(4) J Grandsire(1) T Richard(2) L Tonon(5) C Dubois(2) Y Estornes(2) R Boulos(2) P Bonaventura(1,2) A Page(1) C Gardet(1) V Alcazer(1) S Hughes(6) B Gillet(6) N Gervois(3) N Labarrière(3) Q Wang(7) J Valladeau-Guilemond(1) N Chuvin(2) V Marcel(1,8) J J Diaz(1,8) S Depil(1,2,9)

1:Centre de Recherche en Cancérologie de Lyon, UMR INSERM U1052 CNRS 5286 Université Claude Bernard Lyon 1 Centre Léon Bérard; Lyon, France.; 2:ErVimmune; Lyon, France.; 3:INCIT, UMR1302 INSERM; Nantes, France.; 4:CNRS-Institut de Biologie et Chimie des Protéines UMR5086; Lyon, France.; 5:Synergie Lyon Cancer; Lyon, France.; 6:Institut de Génomique Fonctionnelle de Lyon; Lyon, France; 7:Complete Omics; Baltimore, MD, USA.; 8:LYriCAN+, DevWeCAN and PLASCAN; Lyon, France.; 9:Centre Léon Bérard; Lyon, France.

Translation is dysregulated in cancer cells with an increase of translational defects. We proposed that these translational alterations in cancer produce shared and immunogenic tumor-specific epitopes derived from oncogenes such as c-Myc, which represent a new family of targets for cancer immunotherapy. An in silico-based method identified potential neoepitopes derived from alternative open-reading frames of c-Myc and selected 2 candidates with evidence of specific translation in tumors in proteomic databases. Targeted immunopeptidomics confirmed the presence of the PR3 epitope on HLA molecules on the surface of tumor cell lines but not on normal primary cells. RNAseq analysis and a bicistronic reporter assay confirmed the translational origin of PR3. PR3-specific T cells were found among tumor infiltrating lymphocytes from 6/22 (27%) colon cancer samples, suggesting that PR3 is presented and immunogenic in cancer patients. PR3-specific CD8+ T cell clones of high functional avidity were generated by in vitro priming of T cells by dendritic cells from healthy donors. To assess the therapeutic potential of targeting the PR3 neoepitope, we genetically engineered T cells to express a PR3-specific TCR (TCR-T cells). After validating their functionality and TCR specificity, we confirmed that these TCR-T cells are cytotoxic against tumor cells endogenously presenting PR3, while sparing normal primary cells. We also demonstrated the in vivo antitumor activity of these PR3-specific TCR-T cells using the immuno-AVI-cellDXᵀᴹ model and NSG mice transplanted with tumor cells expressing PR3. Our results provide preclinical rationale for developing T-cell based immunotherapies targeting this c-MYC-derived neoepitope.