Abstract B007: Targeting the evolving immunopeptidome of metastatic colorectal cancer

Abstract Chimeric antigen receptor (CAR) T cell therapies have achieved limited success in solid tumors, in part due to challenges in identifying cancer-specific targets. Investigating the immunopeptidome, peptides presented by human leukocyte antigen (HLA) class I molecules, offers an opportunity to expand the repertoire of targetable antigens. Recent findings reveal that metastatic colorectal cancer (mCRC) cells adopt a highly stereotyped fetal-like phenotype, characterized by the activation of a developmental WNT-signaling signature as a mechanism of cell-fate reprogramming. This transcriptional signature, accentuated in metastasis-initiating cells and conserved across diverse patients, is hypothesized to translate into a cancer-specific immunopeptidome. Utilizing an integrated platform, we collected and analyzed resected normal colon, primary tumor, and metastatic lesions from CRC patients, establishing patient-derived organoids (PDOs) that recapitulate CRC cell states ex vivo. Mass spectrometry profiling of PDOs from HLA-A*02:01+ patients identified peptide targets derived from fetal WNT-pathway gene states, referred to as oncofetal protein 1 (OFP1). These peptides were specific to CRC, absent in healthy tissues, and demonstrated immunogenicity through healthy donor T cell reactivity and expansion assays. To further harness these findings, we aim to systematically profile the immunopeptidome evolution from normal colon to metastatic CRC to identify conserved CRC-specific peptides for therapeutic targeting. Furthermore, we employed large-scale yeast display technology to isolate peptide-centric T cell receptor mimics (TCRms) that specifically recognize OFP1 peptides presented by HLA-A*02:01. Preliminary results demonstrate the successful isolation of OFP1-specific, HLA-A02:01-restricted TCRms, paving the way for the development of TCRm-based CAR T cells tailored for CRC therapy. This work provides the first comprehensive atlas of immunopeptidome evolution in CRC, elucidates CRC-specific intracellular molecular signatures as potential therapeutic targets, and advances the preclinical development of TCRm-engineered CAR T cells, paving the way for precision immunotherapies in metastatic CRC. Citation Format: Jaeyop Lee, David A Scheinberg, Karuna Ganesh. Targeting the evolving immunopeptidome of metastatic colorectal cancer [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B007.