Abstract I05: Heterocellular interactions in the tumor microenvironment

Abstract

Abstract Pancreatic ductal adenocarcinoma (PDA) is characterized by a heterocellular microenvironment, exhibiting tumor-promoting as well as tumor-restrictive effects. Tumor cells coerce host cells, such as fibroblasts and myeloid cells, to remodel the stroma, which results in altered stiffness, cell-cell signaling, and modified tumor cell function. The rules governing tumor-stromal interactions are currently not clearly defined. To demark and characterize the cellular components of the tumor microenvironment we devised protein-based marker panels for single-cell analysis by cytometry by time of flight (CyTOF), specifically aimed at defining populations of cancer-associated fibroblast (CAFs). Importantly, we employed cell surface markers, enabling isolation and functional characterization of identified stromal populations. Using these panels, we interrogated tumors from the pdx1-cre; LSL-KrasG12D/+; LSL-Trp53R172H/+ (KPC) genetic engineered model of pancreatic cancer. We observe previously defined CAF populations expressing markers for myofibroblastic CAFs (myCAF); inflammatory CAFs (iCAF) and antigen presenting CAFs (apCAF). In addition to these CAF populations, we observe that differential expression of the auxiliary receptor for the TGFβ receptor complex, endoglin (CD105), demarks two distinct fibroblast populations that are present in murine and human PDA. In addition, we observe CD105-positive (CD105+) and -negative (CD105-) fibroblasts in normal healthy pancreas, liver, and lung, indicating that the presence of these CAFs in tumors is likely due to local expansion. Isolated fibroblasts preserve differential expression of CD105+ and CD105- throughout extended in vitro culture, co-culture, and treatment with regulators of fibroblast function, indicating that CD105 may act as a bona fide lineage marker. We find that while both CD105+/- lineages are able to adapt a general myCAF or iCAF polarization, they show distinct regulation of specific genes. 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: Claus Jorgensen. Heterocellular interactions in the tumor microenvironment [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 I05.