Inflammatory changes play an important role in tumorigenesis, and patients with chronic inflammatory bowel disease (IBD) are at an increased risk of developing colitis-associated cancer (CAC). However, the cellular contributions of these inflammatory changes in CAC are not well defined. The TNFSF15 locus harbors significant polymorphisms associated with IBD and the protein product of TNFSF15 (called TNF-like cytokine 1a or TL1A) regulates innate and adaptive immunity. Therefore, the main objective of this work is to investigate the potential role for TL1A in CAC and the cellular contribution by intestinal ILC3s. Using the human atlas protein database and single cell data, we found that TL1A is expressed in tumor associated macrophages and that high expression of TNFSF15 correlated with reduced survival in colorectal cancer patients. To test the functional role for TL1A in tumorigenesis, we used the well-established AOM/DSS model of CAC in mice deficient for TL1A or its receptor (called death receptor 3 or DR3). We found that TL1A and DR3-deficient mice had a significant reduction in tumor number compared to heterozygous littermate controls. To evaluate the contribution of innate lymphocytes, we used DR3-deficient mice on a RAG-deficient background in our AOM/DSS model. Even in the absence of B and T cells, DR3-deficient mice had a significant reduction in tumor burden, which was confirmed to be ILC3 dependent using DR3 deficient mice specifically only on ILC3s. Neutrophil infiltration was reduced in the colon of DR3-deficient mice in our AOM/DSS model as well as on models of innate inflammatory colitis. Neutrophil depletion also resulted in a significant reduction of tumor numbers in our CAC model in a DR3 dependent manner. In vitro co-culture of intestinal type 3 innate lymphoid cells and bone marrow derived neutrophils revealed a role for ILC3 derived GM-CSF in activating neutrophils in a TL1A dependent manner. Furthermore, RNA-seq of TL1A-ILC3 stimulated neutrophils revealed a transcriptional reshape into an inflammatory/tumor promoting phenotype. These transcriptional signatures were evident in humans with UC treated with anti-TL1A. Deletion of DR3 specifically on ILC3s resulted in a significant reduction in tumor numbers, highlighting a role for ILC3s in TL1A dependent tumorigenesis. Intestinal inflammation as well as in vivo activation with a DR3 agonist also impacted bone marrow emergency granulopoiesis by expanding both mature neutrophils and granulocyte-macrophage progenitors (GMPs). We also found that IBD patients that have the risk allele for TNFSF15 displayed increase levels of neutrophils and GMPs in the blood. Our data reveals a new link between intestinal ILC3 production of GM-CSF and neutrophil activation that promotes CAC and bone marrow granulopoiesis.

Ian Wicks

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