CD8+ T-cell Immune Surveillance against a Tumor Antigen Encoded by the Oncogenic Long Noncoding RNA PVT1.

CD8+ T cells recognize peptides displayed by HLA class I molecules on cell surfaces, monitoring pathologic conditions such as cancer. Advances in proteogenomic analysis of HLA ligandomes have demonstrated that cells present a subset of cryptic peptides derived from noncoding regions of the genome; however, the roles of cryptic HLA ligands in tumor immunity remain unknown. In the current study, we comprehensively and quantitatively investigated the HLA class I ligandome of a set of human colorectal cancer and matched normal tissues, showing that cryptic translation products accounted for approximately 5% of the HLA class I ligandome. We also found that a peptide encoded by the long noncoding RNA (lncRNA) PVT1 was predominantly enriched in multiple colorectal cancer tissues. The PVT1 gene is located downstream of the MYC gene in the genome and is aberrantly overexpressed across a variety of cancers, reflecting its oncogenic property. The PVT1 peptide was recognized by patient CD8+ tumor-infiltrating lymphocytes, as well as peripheral blood mononuclear cells, suggesting the presence of patient immune surveillance. Our findings show that peptides can be translated from lncRNAs and presented by HLA class I and that cancer patient T cells are capable of sensing aberrations in noncoding regions of the genome.

Proteogenomic identification of an immunogenic HLA class I neoantigen in mismatch repair-deficient colorectal cancer tissue.

Although CD8+ T cells recognize neoantigens that arise from somatic mutations in cancer, only a small fraction of nonsynonymous mutations give rise to clinically relevant neoantigens. In this study, HLA class I ligandomes of a panel of human colorectal cancer (CRC) and matched normal tissues were analyzed using mass spectrometry-based proteogenomic analysis. Neoantigen presentation was rare; however, the analysis detected a single neoantigen in a mismatch repair-deficient CRC (dMMR-CRC) tissue sample carrying 3967 nonsynonymous mutations, where abundant tumor-infiltrating lymphocytes (TILs) and inflamed gene expression status were observed in the tumor microenvironment (TME). Using the HLA class I ligandome data and gene expression profiles, a set of nonmutated tumor-associated antigen (TAA) candidates was concomitantly identified. Interestingly, CD8+ TILs predominantly recognized the detected neoantigen over the array of TAA candidates. Neoantigen-reactive CD8+ TILs showed PD-1 positivity and exhibited functional and specific responses. Moreover, T cell receptor (TCR) profiling identified the sequence of the neoantigen-reactive TCR clonotype and showed its expansion in the TME. Transduction of the sequenced TCR conferred neoantigen specificity and cytotoxicity to peripheral blood lymphocytes. The proteogenomic approach revealed the antigenic and reactive T cell landscape in dMMR-CRC, demonstrating the presence of an immunogenic neoantigen and its potential therapeutic applications.