IgG response to MHC class I epitope peptides is a quantitative predictive biomarker in the early course of treatment of colorectal cancer using therapeutic peptides

Cancer vaccines have been developed as a new therapeutic approach, however, their clinical benefit remains limited. We previously performed a phase II study for advanced colorectal cancer (CRC) using five human leukocyte antigen (HLA-A*24:02)-restricted peptides derived from kinase of the outer chloroplast membrane 1, translocase of outer mitochondrial membrane 34 (TOMM34), ring finger protein 43 (RNF43), vascular endothelial growth factor receptor 1 (VEGFR1) and VEGFR2. In the present study the relationship between overall survival (OS) and several biomarkers, including cytotoxic T lymphocyte (CTL) and immunoglobulin G (IgG) responses to these five peptides, was investigated. In 89 advanced CRC patients treated with a combination therapy consisting of these five peptides and oxaliplatin-based chemotherapy, plasma was collected before and after 3 months of vaccine administration. IgGs reactive to each of the five peptides were assessed using the multiplex bead suspension Luminex system. Antigen-specific T-cell responses were estimated by enzyme-linked immunoSpot assay. Plasma levels of TOMM34 IgG (P