Abstract 7464: Tertiary lymphoid structures in pancreatic cancer: Biomarkers of immunogenic patients or direct contributors to anti-tumor immunity

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a cancer with low survival rates and currently no immunotherapy options. However, many tumors from PDAC patients can be heavily infiltrated with T and B cells associated with favorable survival outcomes indicating anti-tumor immunity is functional in certain patients. In some of these lymphocyte-inflamed PDAC tumors, spontaneous organization of tertiary lymphoid structures (TLS) is evident upon surgical resection and these patients have a clear survival advantage. TLS are predictive of immune checkpoint blockade response in some cancer types, yet PDAC patients, with or without TLS, are still insensitive to these strategies. To address this paradox, we evaluated surgically resected PDAC tumors from previously untreated patients and discovered that tumors with TLS (TLS+) recruited T and B cells with specific anti-tumor and memory phenotypes suggesting immunosurveillance of disease was enhanced. Furthermore, a subset of TLS+ patients contained germinal centers and improved humoral immune function corresponding to an increased neoantigen burden and long-term survival. When assessing gene expression differences between TLS+ and TLS- patients, operable inflammatory and immunosuppressive pathways emerged that could be therapeutically exploited to activate TLS neogenesis. To address these mechanistic questions, we have developed a method for inducing TLS formation in implantable mouse PDAC tumors in the orthotopic setting utilizing an antibody that agonizes the lymphotoxin beta receptor (LTBR) in mice bearing established PDAC tumors. These TLS are complexed with T cells, B cells, CXCL13+ cells, and PNAd+ HEV associated with reduced tumor growth, presence of lymphocyte-recruiting cancer associated fibroblasts and increases in anti-tumor T and B cell phenotypes. Interestingly, some mouse PDAC cell lines are resistant to TLS formation by LTBR agonism while others are susceptible offering a model to study patient heterogeneity. We will use this TLS+ PDAC mouse model to address how TLS may directly improve antigen-specific T cell and B cell immunity and elucidate the pathways that regulate TLS formation. These data will offer new strategies to overcome immunotherapy resistance in cancer patients. Citation Format: Shrijan Khanal, Olivia Harder, Elijah Kirschstein, Morgan Mack, Carl Ware, Michael Gough, Kristina Young, Andrew J. Gunderson. Tertiary lymphoid structures in pancreatic cancer: Biomarkers of immunogenic patients or direct contributors to anti-tumor immunity abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 7464.