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MHCquant: Automated and reproducible data analysis for immunopeptidomics

ABSTRACT: Personalized multi-peptide vaccines are currently being discussed intensively for tumor immunotherapy. In order to find epitopes - short, immunogenic peptides - suitable to elicit an immune response, human leukocyte antigen-presented peptides from cancer tissue samples are purified using immunoaffinity purification and analyzed by high performance liquid chromatography coupled to mass spectrometry. Here we report on a novel computational pipeline to identify peptides from large-scale immunopeptidomics raw data sets. In the conducted experiments we benchmarked our workflow to other existing mass spectrometry analysis software and achieved higher sensitivity. A dataset of 38 HLA immunopeptidomics raw files of peripheral blood mononuclear cells (PBMCs) from 10 healthy volunteers and 4 JY cell lines was used to assess the performance of the pipeline at each processing step. In addition, 66 isotope labeled known HLA-presented peptides were spiked into the JY cell extracts decreasing in concentration by log10 steps from 100 fmol to 0.1 fmol.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (ncbitaxon:9606)

SUBMITTER: Professor Oliver Kohlbacher

PROVIDER: MSV000098352 | MassIVE | Fri Jun 27 04:19:00 BST 2025

SECONDARY ACCESSION(S): PXD011628

REPOSITORIES: MassIVE

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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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MHCquant: Automated and reproducible data analysis for immunopeptidomics

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