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DNMT and HDAC inhibition induces immunogenic neoantigens from human endogenous retroviral element-derived transcripts

ABSTRACT: Immunotherapies targeting cancer-specific neoantigens have revolutionized the treatment of cancer patients. Recent evidence suggests that epigenetic therapies synergize with immunotherapies, mediated bythe de-repression of endogenous retroviral element (ERV)-encoded promoters, and the initiation of transcription. Here, we use deep RNA sequencing from cancer cell lines treated with DNA methyltransferase inhibitors (DNMTi) and/or Histone deacetylase transferase inhibitors (HDACi), to assemble a de novo transcriptome and identified 3,023 ERV-derived, treatment-induced novel polyadenylated transcripts (TINPATs), encoding for 61,426 open reading frames. Using Immunopeptidomics, we further demonstrate the human leukocyte antigen (HLA) presentation of treatment-induced neoepitopes (t-neoepitopes) derived from TINPATs. We illustrate the potential of the identified t-neoepitopes to elicit a T-cell response and cancer cell killing. The presence of t-neoepitopes was further verified in AML patient samples 48/96 h after in vivo treatment with the DNMT inhibitor Decitabine. Our findings highlight a novel mechanism of ERV-derived neoantigens in epigenetic and immune therapies.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture, Blood

SUBMITTER: Jens Bauer

LAB HEAD: Professor Juliane Walz

PROVIDER: PXD035750 | Pride | 2023-08-18

REPOSITORIES: Pride

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Project description:Background: Patient derived organoids (PDOs) can be established from colorectal cancers as in vitro models to interrogate cancer biology and its clinical relevance. We applied mass spectrometry (MS) immunopeptidomics to investigate neoantigen presentation and whether this can be augmented through interferon gamma (IFN) or MEK-inhibitors. Methods: Four PDOs from chemotherapy refractory and one from a treatment naïve CRC were expanded to replicates with 100 million cells each, and HLA class I and class II peptide ligands were analysed by MS. Results: We identified an average of 9,936 unique peptides per PDO which compares favourably against published immunopeptidomics studies, suggesting high sensitivity. Loss of heterozygosity of the HLA locus was associated with low peptide diversity in one PDO. Peptides from genes without detectable expression by RNA-sequencing were rarely identified by MS. Only 3 out of 612 non-silent mutations encoded for neoantigens that were detected by MS. Treatment of four PDOs with IFN upregulated HLA class I expression and qualitatively changed the immunopeptidome, with increased presentation of IFN-inducible genes. HLA class II presented peptides increased on average 16-fold with IFN treatment. MEK-inhibitor treatment showed no consistent effect on class I or II HLA expression or the peptidome. Importantly, no additional HLA class I or II presented neoantigens became detectable with any treatment. Conclusions: Only 3 out of 612 non-synonymous mutations encoded for neoantigens that were detectable by MS. Although MS has sensitivity limits and biases, and likely underestimated the true neoantigen burden, this established a lower bound of the percentage of non-silent mutations that encode for presented neoantigens, which may be as low as 0.5%. This could be a reason for the poor responses of non-hypermutated CRCs to immune checkpoint inhibitors. MEK-inhibitors recently failed to improve checkpoint-inhibitor efficacy in CRC and the observed lack of HLA upregulation or improved peptide presentation may explain this.

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DNMT and HDAC inhibition induces immunogenic neoantigens from human endogenous retroviral element-derived transcripts

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