Abstract 2667: TM4SF1 as a novel tumor-associated antigen in biliary tract cancers targetable by immune effector cell therapy

Abstract Biliary tract cancers (BTC) are a rare set of genetically heterogeneous and aggressive malignancies associated with late presentation, poor prognosis and limited effective therapies. Thus, there is an unmet clinical need for the development of novel therapeutic strategies. Identification of uniquely expressed cell-surface tumor-associated antigens (TAA) holds promise in epithelial tumors more generally, as they can serve as ligands for a variety of therapeutics, including CAR-T cell therapy. However, TAA identification in BTCs has been limited by expression in normal liver tissue. Here, we identify the cell-surface protein transmembrane 4 L six family member 1 (TM4SF1) as a potential BTC TAA targetable by CAR-T therapy. We find TM4SF1 expression is upregulated in BTC relative to normal hepatic/biliary tissue at the mRNA level in the TCGA dataset. Correspondingly, we find that TM4SF1 in primary BTC archival tissue is upregulated at the protein level using immunohistochemistry. To validate TM4SF1 as a targetable TAA in BTC, we show that TM4SF1-directed CAR-T cells demonstrate robust, dose-dependent growth inhibition of human-derived BTC cell lines in vitro and significant anti-tumor activity in a heterotopic BTC cell line-derived xenograft model in vivo. Together, our data provide support for TM4SF1 as a promising TAA in BTCs that can be used for the rational development of therapeutic modalities targeting TM4SF1, including CAR-T cells, in a patient population with significant unmet need. Citation Format: Lorraine Nuniz, Franklin Huang. TM4SF1 as a novel tumor-associated antigen in biliary tract cancers targetable by immune effector cell therapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2667.