In recent work, we have developed immunopeptidome-guided peptide vaccines adjuvanted with the novel TLR 1/2 agonist XS15 as an adjuvant,40 which have proven to induce potent and long-lasting CD4+ and CD8+ T-cell responses accompanied by signs of clinical efficacy from preclinical models until phase II clinical evaluation.42 61 Here, we evaluated the potential of the PCI-DB to design personalized peptide vaccines in a retrospective analysis of two patients suffering from metastatic ovarian cancer and prostate cancer, with and without available immunopeptidome data, respectively. The gene discussed is CD4; the disease is prostate cancer.