Abstract PR021: CCR1 expression defines pancreatic tumor associated macrophages and drives their immunosuppressive properties
Authors: Zhang Yaqing , Yan Wei , Brown Kristee L. , Velez-Delgado Ashely , Nwosu Zeribe C. , Donahue Katelyn , Kadiyala Padma , Yang Sion , Avritt Faith R. , He Xi , Espinoza Carlos , di Magliano Marina Pasca 
Published: November 2022

Abstract
The tumor microenvironment of pancreatic ductal adenocarcinoma (PDA) includes abundant fibroblasts and infiltrating immune cells, the latter largely immunosuppressive. Immunotherapy approaches have been ineffective in PDA, pointing to the need for a better understanding of the mechanisms of immunosuppression. We previously identified C-C Motif Chemokine Receptor 1 (CCR1) as overexpressed in macrophages exposed to pancreatic cancer cell conditioned medium in vitro. By single-cell RNA sequencing, we found CCR1 to be expressed by tumor associated macrophages (TAMs) and granulocytes in both human and mouse PDA. Conversely, the ligands for CCR1, C-C Motif Chemokine Ligands (CCLs), are produced by tumor associated fibroblasts. Thus, we sought to investigate the functional role of CCR1 in pancreatic cancer using a combination of genetically engineered mouse models and pharmaceutically approaches. In a first set of experiments, we generated KC;CCR1-/- mice (Ptf1a-Cre;LSL-KrasG12D;CCR1-/-) to determine the requirement of CCR1 during oncogenic KRAS induced pancreatic cancer initiation. We did not observe a difference in PanIN formation/progression in KC;CCR1-/- compared to KC mice. However, we observed increased immune infiltration, including CD8 T cells, in KC;CCR1-/- pancreata. In a second set of experiments, we then orthotopically transplanted two independent mouse pancreatic cancer cells derived from the KPC model in syngeneic CCR1 knockout hosts. We observed reduced tumor growth, which was rescued by CD8 T cell depletion, indicating an increase of anti-tumor immunity in mice lacking CCR1. Consistently, we observed elevated cytotoxic Granzyme B expression, as well as an increase of apoptotic cells in tumors harvested from Ccr1-/- mice. Through mass cytometry (CyTOF) and co-immunofluorescence staining we discovered that tumor associated macrophages from CCR1-/- mice expressed less Arginase 1 and CD206, both immunosuppressive markers, compared to macrophages in wild type tumors. In the last set of experiments, we used the CCR1 inhibitor J-113863, administered to mice following establishment of an orthotopically implanted tumor. Similar to the genetic model, CCR1 inhibition resulted in smaller tumors. Further, targeting CCR1 either genetically or using a CCR1 inhibitor synergizes with anti-PDL1 immune checkpoint blockade to reduce tumor growth. Together, our data is consistent with the notion that tumor associated macrophages lacking CCR1 expression are less immunosuppressive, consequently allowing increased CD8 T cell-mediated anti-tumor immunity. Targeting CCR1 in combination with immune checkpoint blockade improves antitumor efficacy in pancreatic cancer.
Citation Format: Yaqing Zhang, Wei Yan, Kristee L. Brown, Ashely Velez-Delgado, Zeribe C. Nwosu, Katelyn Donahue, Padma Kadiyala, Sion Yang, Faith R. Avritt, Xi He, Carlos Espinoza, Marina Pasca di Magliano. CCR1 expression defines pancreatic tumor associated macrophages and drives their immunosuppressive properties [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr PR021.