Single-cell RNA sequencing and influences of necroptosis-associated myeloid lineages in immune microenvironment of PDAC

e16261 Background: Tumor-infiltrating myeloid cells (TIMs) are abundant in tumor stroma and emerging evidence indicate that the presence of these cells influences clinical outcomes in many cancer types. TIMs play important roles in tumor progression and specific subsets may exhibit divergent anti-tumor or tumor-promoting functions. Currently, the molecular characteristics of TIMs in pancreatic ductal adenocarcinoma (PDAC) largely remain unknown. Like other programmed cell death procedures such as ferroptosis and pyroptosis, necroptosis has recently emerged as an important cellular event that modulates tumorigenesis and tumor progression. Combination of necroptosis and TIMs is of great interest to study the molecular mechanism of clinical outcomes for PDAC patients. Methods: This study enrolled 16 PDAC patients. The scRNA-seq data were obtained from a published dataset and each patient included primary tumor, metastatic tumor, primary tumor-adjacent and PBMC samples. All myeloid cells comprising granulocytes, monocytes, macrophages, and dendritic cells from enrolled patients were extracted for further analysis. We performed comprehensive analysis about the characteristics of myeloid lineages, differentially expressed genes, pathway enrichment analysis and novel cell subtype identification. The necroptosis-associated novel TIMs cell sub-clusters were elucidated in detail. Results: To comprehensively analyze the heterogeneous TIMs microenvironment in PDAC patients using scRNA-seq dataset, we firstly obtained consistently upregulated genes among granulocytes, monocytes, macrophages, and dendritic cell types between tumor samples and non-tumor samples. Those uniquely expressed genes represent different functions in necroptosis-associated TIMs cells. In total, we identified 10 necroptosis-associated upregulated genes in PDAC tumors and 5 upregulated genes in tumor-adjacent and peripheral blood samples, respectively. Based on the cells expressed those necroptosis-related genes, we identified three novel cell populations, including GLUL - SQSTM1 - RTM, HSP90AA1 + HSP90AB1 + mast cells, and JAK3 + TLR4 + CD16 monocytes, which were regulators of immunity either tumor-promoters or tumor-suppressors. Clinical outcomes further supported their function roles in the PDAC tumor microenvironment. Conclusions: This study comprehensively studied the heterogeneity of myeloid microenvironment in PDAC by scRNA-Seq. Several necroptosis-associated genes and myeloid cell sub-clusters were identified and they have prognostic clinical values in PDAC. These preliminary results were helpful for further understanding the molecular mechanism of PDAC treatment strategies.