Abstract PO-046: Dissecting the role of tumor-intrinsic Cxcl1 in mediating immune exclusion in Ras-p53 cooperative pancreatic cancer
Authors: Bianchi Anna , Mehra Siddharth , Dai Daisy , de Castro Silva Iago , Sharma Prateek , Colaprico Antonio , Dosch Austin R. , Singh Samara , Nagathihalli Nagaraj S. , Merchant Nipun B. , Datta Jashodeep 
Published: November 2020

Abstract
INTRODUCTION: Ras-p53 cooperative mutations, which define &gt;50% of human pancreatic ductal adenocarcinoma (PDAC), promote an immune-excluded tumor microenvironment. In Ras-p53 murine models that phenocopy human PDAC, overexpression of the myeloid chemo-attractant Cxcl1 is associated with T-cell exclusion. We sought to dissect the role of tumor-intrinsic Cxcl1 in mediating immune exclusion in Ras-p53 PDAC. METHODS: Single-cell immune deconvolution and Cxcl1 expression were queried in TCGA PDAC samples (n=150). Single-cell RNA sequencing (scRNAseq) data in KrasG12D/+;Trp53fl/+;Pdx1Cre (KPC WT) genetically engineered mice (GEM) were interrogated. CRISPR/Cas9-based genome editing was used to silence Cxcl1 in KPC tumor cells (KPC-Cxcl1KO). Multiparameter flow cytometry-based immunophenotyping of tumor-infiltrating and circulating myeloid/T-cell populations was performed in in-vivo orthotopic models utilizing KPCWT / KPC-Cxcl1KO cells. RESULTS: In human TCGA samples, Cxcl1 overexpression was strongly associated with expression of its cognate receptor CXCR2, reduced CD4+/CD8+ T-cells, and increased CD33+ myeloid-derived suppressor cells (MDSCs). In KPC GEMs, scRNAseq revealed that CXCR2 expression was exclusively present on the polymorphonuclear MDSC subset (PMN-MDSC). Exogenous Cxcl1 conditioning in murine bone marrow-derived cells induced PMN-MDSC polarization and upregulated CXCR2. Genetic ablation of Cxcl1 in KPC tumor cells disrupted transwell migration of splenocyte-enriched MDSC in-vitro; this effect was dependent on CXCR2 expression on MDSCs. There was a dramatic reduction in tumor weights and metastatic outgrowth (p&lt;0.0001), as well as circulating PMN-MDSC and CXCR2+-MDSC populations in KPC-Cxcl1KO compared with KPCWT mice (p=0.0006). Significantly fewer PMN-MDSC and M2-like macrophages infiltrated KPC-Cxcl1KO tumors, which was accompanied by dramatically higher CD4+/CD8+ T-cell infiltration (p&lt;0.0001). While cytolytic effector CD8+ T-cell populations (CD44+62L-CD107a+) remained unchanged, non-cytolytic “exhausted” PD-1+CD8+ T-cells (PD-1+CD107a-) increased in KPC-Cxcl1KO vs. KPCWT tumors, providing rationale for addition of checkpoint blockade to reverse T-cell exhaustion. CONCLUSION: Tumor-intrinsic Cxcl1 appears a major contributor to immune exclusion in Ras-p53 cooperative PDAC. Targeting Cxcl1 represents a promising strategy to overcome MDSC-mediated immunosuppression and improve susceptibility to checkpoint blockade in PDAC.
Citation Format: Anna Bianchi, Siddharth Mehra, Daisy Dai, Iago de Castro Silva, Prateek Sharma, Antonio Colaprico, Austin R. Dosch, Samara Singh, Nagaraj S. Nagathihalli, Nipun B. Merchant, Jashodeep Datta. Dissecting the role of tumor-intrinsic Cxcl1 in mediating immune exclusion in Ras-p53 cooperative pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-046.