Immunopeptidomic Profiling of HLA‐A2‐Positive Triple Negative Breast Cancer Identifies Potential Immunotherapy Target Antigens

The recent development in immune checkpoint inhibitors and chimeric antigen receptor (CAR) T‐cells in the treatment of cancer has not only demonstrated the potency of utilizing T‐cell reactivity for cancer therapy, but has also highlighted the need for developing new approaches to discover targets suitable for such novel therapeutics. Here we analyzed the immunopeptidomes of six HLA‐A2‐positive triple negative breast cancer (TNBC) samples by nano‐ultra performance liquid chromatography tandem mass spectrometry (nUPLC‐MS(2)). Immunopeptidomic profiling identified a total of 19 675 peptides from tumor and adjacent normal tissue and 130 of the peptides were found to have higher abundance in tumor than in normal tissues. To determine potential therapeutic target proteins, we calculated the average tumor‐associated cohort coverage (aTaCC) that represents the percentage coverage of each protein in this cohort by peptides that had higher tumoral abundance. Cofilin‐1 (CFL‐1), interleukin‐32 (IL‐32), proliferating cell nuclear antigen (PCNA), syntenin‐1 (SDCBP), and ribophorin‐2 (RPN‐2) were found to have the highest aTaCC scores. We propose that these antigens could be evaluated further for their potential as targets in breast cancer immunotherapy and the small cohort immunopeptidomics analysis technique could be used in a wide spectrum of target discovery. Data are available via ProteomeXchange with identifier PXD009738.