Single-Cell Transcriptomics of Pancreatic Cancer Precursors Demonstrates Epithelial and Microenvironmental Heterogeneity as an Early Event in Neoplastic Progression

Abstract

Purpose: Early detection of pancreatic ductal adenocarcinoma (PDAC) remains elusive. Precursor lesions of PDAC, specifically intraductal papillary mucinous neoplasms (IPMNs), represent a bona fide pathway to invasive neoplasia, although the molecular correlates of progression remain to be fully elucidated. Single-cell transcriptomics provides a unique avenue for dissecting both the epithelial and microenvironmental heterogeneities that accompany multistep progression from noninvasive IPMNs to PDAC. Experimental Design: Single-cell RNA sequencing was performed through droplet-based sequencing on 5,403 cells from 2 low-grade IPMNs (LGD-IPMNs), 2 high-grade IPMNs (HGD-IPMN), and 2 PDACs (all surgically resected). Results: Analysis of single-cell transcriptomes revealed heterogeneous alterations within the epithelium and the tumor microenvironment during the progression of noninvasive dysplasia to invasive cancer. Although HGD-IPMNs expressed many core signaling pathways described in PDAC, LGD-IPMNs harbored subsets of single cells with a transcriptomic profile that overlapped with invasive cancer. Notably, a proinflammatory immune component was readily seen in low-grade IPMNs, composed of cytotoxic T cells, activated T-helper cells, and dendritic cells, which was progressively depleted during neoplastic progression, accompanied by infiltration of myeloid-derived suppressor cells. Finally, stromal myofibroblast populations were heterogeneous and acquired a previously described tumor-promoting and immune-evading phenotype during invasive carcinogenesis. Conclusions: This study demonstrates the ability to perform high-resolution profiling of the transcriptomic changes that occur during multistep progression of cystic PDAC precursors to cancer. Notably, single-cell analysis provides an unparalleled insight into both the epithelial and microenvironmental heterogeneities that accompany early cancer pathogenesis and might be a useful substrate to identify targets for cancer interception. See related commentary by Hernandez-Barco et al., p. 2027

CAF Subpopulations: A New Reservoir of Stromal Targets in Pancreatic Cancer

“…Interestingly, Bernard et al demonstrated that microenvironmental heterogeneity occurs in premalignancy and throughout cancer progression [61]. This study examined iCAF and myCAF populations in PDAC and in precursor low-grade and high-grade intraductal papillary mucinous neoplasms (LG-and HG-IPMN) [61].…”

“…iCAFs were only apparent in PDAC, whereas myCAFs were lowly abundant in LG-IPMN and highly abundant in HG-IPMN, indicating that myCAF activation can also occur in the non-invasive setting. Interestingly, the increase in iCAFs coincided with a clearly defined switch from immunosurveillance (LG-IPMN) to immunosuppression (PDAC) [61]. Considering that iCAFs produce high levels of chemokines and cytokines that are involved in tumourigenesis and disease progression, it is likely that these cells are also responsible for aggressive tumour spread, although this correlation has yet to be explicitly elucidated.…”

Stem cells in cancer initiation and progression

“…Similarly, solid cancers can alter the metastatic niche even before colonization (Kaplan et al, 2005; Costa-Silva et al, 2015; Olmeda et al, 2017). Single-cell sequencing of primary human breast, lung, and pancreatic cancers has revealed heterogeneity not only in the cancer populations but also in immune and other cells of the microenvironment (Bartoschek et al, 2018; Bernard et al, 2019; Elyada et al, 2019; Lawson et al, 2018; Ma et al, 2019; Wagner et al, 2019). Defining the spatial localization of CSCs with respect to specific niche cells, and understanding how these interactions contribute to cancer progression and response to therapy, will be exciting future avenues of work.…”

IL1-Induced JAK/STAT Signaling Is Antagonized by TGFβ to Shape CAF Heterogeneity in Pancreatic Ductal Adenocarcinoma

“…Importantly, the presence of iCAF and myCAF populations in human PDAC Cancer Research. in vivo has been recently confirmed (20). However, the signals that drive the formation of these distinct populations are not known.…”