Multimodal mapping of the tumor and peripheral blood immune landscape in human pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by an immune-suppressive tumor microenvironment that renders it largely refractory to immunotherapy. We implemented a multimodal analysis approach to elucidate the immune landscape in PDA. Using a combination of CyTOF, single-cell RNA sequencing and multiplex immunohistochemistry on patient tumors, matched blood and non-malignant samples, we uncovered a complex network of immune-suppressive cellular interactions. These experiments revealed heterogeneous expression of immune checkpoint receptors in individual patients' T cells and increased markers of CD8(+) T cell dysfunction in the advanced disease stage. Tumor-infiltrating CD8(+) T cells had an increased proportion of cells expressing an exhausted expression profile that included upregulation of the immune checkpoint TIGIT, a finding that we validated at the protein level. Our findings point to a profound alteration of the immune landscape of tumors, and to patient-specific immune changes that should be taken into account as combination immunotherapy becomes available for pancreatic cancer. Using single-cell RNA sequencing, CyTOF and multiplex immunohistochemistry, Steele et al. survey the immune landscape in pancreatic cancers, adjacent tissue and blood, observing heterogeneous immune checkpoint receptor expression within patients.