Abstract C068: Phenotypic plasticity and functional divergence of neutrophilic MDSCs in pancreatic cancer

Abstract BACKGROUND: Circulating polymorphonuclear neutrophils (PMN) traffic to pancreatic cancer (PDAC)-derived cues, where they acquire specialization as myeloid-derived suppressor cells (MDSC) to exert immune tolerance and stromal inflammation. We sought to dissect the developmental heterogeneity of PMN/MDSCs during PDAC tumorigenesis, molecular networks underlying these fate transitions, and their correlation with oncologic outcomes in PDAC patients. METHODS:Pancreatic tumors & spleens from Ptf1a Cre/+;LSL-Kras G12D/+;Tgfbr2 fl/fl (PKT) mice at 4 and 6 wks of age, along with pancreata/spleens from age-matched littermates, were subjected to single-cell RNA sequencing (scRNAseq). Clustering and splicing kinetics identified distinct populations of circulating and tissue-resident PMN/MDSCs. Ingenuity Pathway Analysis (IPA) nominated unique surface markers for each subset, which was validated by flow cytometry. Paired RNA-ATAC sequencing and functional studied were performed in marker- sorted PMNs. RESULTS: scRNAseq of PKT tumors/spleens revealed striking temporal and phenotypic heterogeneity in PMN subclusters with PDAC tumorigenesis. RNA velocity analysis identified distinct terminal-state (TS) populations in tumors and circulation. The intratumoral-TS fate of PMNs resembled MDSC-like specialization, with enrichment of gene programs indicating suppressive function (Tnf,Il1b,Cd14). Conversely, spleen-TS PMNs showed imprinting of trafficking programs (Cxcr2,Il1rap,Gab2). Intriguingly, a discrete PMN cluster in both spleen and tumors displayed upregulated MHC-II and co-stimulatory molecule genes (H2-Ab,Cd79a,Cd80). IPA of differentially expressed genes with transmembrane localization nominated Cd170, Cd162, and MHC-II as surface markers for tumor-TS, spleen-TS, and MHC-II PMN subsets, which were validated by flow cytometry. RNAseq of Cd170/SiglecF+ intratumoral MDSCs revealed upregulation in inflammatory and pro-survival signaling pathways (Akt/mTor-PID, Il1-KEGG, Myc targets-HALLMARK), with TNF as top predicted upstream regulator by IPA. Enrichment in fibrosis-related genes were supported by Smad4 motif enrichment in Cd170+ RNA/ATAC-seq, suggesting novel profibrotic function. Transcription factor (TF) inference in MHC-II+ PMNs revealed high activity scores for TFs (Rora,Irf1) regulating antigen presentation pathways. Ex vivo co-culture of T-cells with marker-sorted PMNs showed reduced T-cell proliferation/activation preferentially with Cd170+ MDSCs, which were partially and completely reversed upon Cd162+ and MHC-II+ PMN co-culture, respectively. In human PDAC scRNAseq data, increased ratio of CD170:MHC-II PMN correlated with chemoresistance and poor survival. CONCLUSIONS: Phenotypic plasticity of PMNs during PDAC progression drive functional divergence and terminal fate determinism in distinct tissue niches. Relative dosage of MDSCs to MHC-II+ PMN may have prognostic and predictive value. Mechanisms governing fate transitions in PMN subsets could pave the way for future therapeutic targets to overcome immunotherapy resistance in PDAC. Citation Format: Anna Bianchi, Manan Patel, Da Yin, Haleh Amirian, Karthik Rajkumar, Andrew Mark Adams, Erin Dickey, Harper Margaret Marsh, Nagaraj Nagathihalli, Nipun Merchant, Dmitry Gabrilovich, Jashodeep Datta. Phenotypic plasticity and functional divergence of neutrophilic MDSCs in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C068.