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Multimodal Mapping of the Immune Landscape in Human Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by an immune-suppressive tumor microenvironment that has rendered it largely refractory to immunotherapy. We used single-cell RNA sequencing on patient tumors and matched blood, and we uncovered a previously unappreciated, complex environment of immune-suppressive cellular interactions. These experiments reveal immune checkpoint expression heterogeneity on individual patient T cells, with corresponding ligands on neoplastic and myeloid cells. TIGIT was upregulated on tumor infiltrating CD8+ T cells and was the only checkpoint receptor consistently expressed by exhausted CD8+ T cells. Clinical annotation of the samples revealed that the exhausted signature is most prominent in patients with advanced stages of disease. Our findings suggest individualized combination therapy, involving anti-TIGIT therapies, may be necessary to extend the benefits of immunotherapy to pancreatic cancer patients.