Abstract B63: Mass cytometry identifies two distinct fibroblast lineages in pancreatic tumors that differentially regulate antitumor immunity
Authors: Hutton Colin , Heider Felix , Veluscek Giulia , Zhang Xiaohong , Morton Jennifer , Jorgensen Claus 
Published: March 2020

Abstract
Pancreatic ductal adenocarcinoma (PDA) is defined by an extensive, fibroblast-rich desmoplasia. Recent single-cell RNAseq studies in pancreatic cancer and other tumor types have described extensive transcriptional heterogeneity within the fibroblast compartment on par with the transcriptional heterogeneity observed in immune compartments. These studies have also provided further evidence of the remarkable phenotypic plasticity of fibroblasts, which may switch between a “myofibroblast-like” (MyCAF) state and an “inflammatory-like” (iCAF) state. Nevertheless, the functional implications of individual fibroblast populations, and associated markers, remain incompletely characterized. Delineating how subsets of fibroblasts might influence PDA tumor function is severely hindered by a lack of useful fibroblast markers, precluding live cell isolation and detailed mechanistic studies. To address this, we have developed a novel, 42-marker fibroblast-specific mass cytometry panel, which has enabled us to annotate the PDA tumor microenvironment at single-cell resolution and interrogate fibroblast populations directly from tumors. We have identified several markers that are unique to subpopulations of fibroblasts within tumors and provide evidence that differential expression of the auxiliary receptor for the TGFβ receptor complex, endoglin (CD105), demarks two fibroblast populations that are present in murine and human PDA tumors. We show that CD105+/- fibroblast populations are present in healthy murine and human pancreas, suggesting their presence in tumors is likely due to local expansion as opposed to recruitment from distal sites. CD105+/- fibroblasts retain differential CD105 expression throughout extended passaging and activation, indicating CD105 as a marker of distinct, stable fibroblast lineages, as opposed to different phenotypic “states.” Interestingly, we also observe stable CD105+/- fibroblast lineages in the liver and lung, which are the major and minor sites of metastatic colonization in PDA, respectively. We find that while both CD105+/- lineages are able to adopt a general MyCAF or iCAF polarization, they show distinct regulation of specific genes. Furthermore, using a syngeneic subcutaneous co-transplant model we demonstrate that CD105+ fibroblasts are tumor-promoting, while CD105- fibroblasts are highly tumor-restrictive. Interestingly, both mechanisms are mediated by differential regulation of CD8+ T cell-dependent adaptive immunity. Together these data define two novel, functionally distinct fibroblast populations in PDA with pro- or antitumorigenic effects.
Citation Format: Colin Hutton, Felix Heider, Giulia Veluscek, Xiaohong Zhang, Jennifer Morton, Claus Jorgensen. Mass cytometry identifies two distinct fibroblast lineages in pancreatic tumors that differentially regulate antitumor immunity [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr B63.