Abstract 6883: Investigation of tumor-immune interactions in pediatric sarcomas using single-cell multi-omics
Authors: Zhang Zhan , Ahn Kyung Jin , Chen Changya , Biyik Sit Rumeysa , Mohei Hesham , Lockhart Brian , Haldar Malay , Bernt Kathrin , Pillai Vinodh , Tan Kai 
Published: March 2024

Abstract
Background: Pediatric sarcoma represents the second most common solid tumor in children. Despite advances in multimodal therapies, one-third of sarcoma patients do not survive the disease. Over the past few decades, the development of novel therapeutic strategies for sarcoma has been impeded by an insufficient understanding of the tumor microenvironment (TME). In particular, the potential of immunotherapy remains constrained by the gap of knowledge about the molecular and functional phenotypes of the immune cells in the sarcoma TME.
Methods: To address this knowledge gap, we collected treatment-naïve tumor samples from 32 patients with five pediatric sarcoma subtypes. We employed a single-nuclei RNA+ATAC-Seq multi-omics assay to comprehensively characterize the transcriptomic and epigenomic heterogeneity of tumor and immune cells within the sarcoma TME.
Results: Our analysis revealed that tumor-associated macrophages (TAMs) were the most abundant immune cell type in the sarcoma TME. We identified seven distinct TAM subpopulations, each exhibiting unique gene expression and chromatin accessibility patterns. Among these, TAM subsets with higher expression of SPP1 and C1QC genes displayed the strongest immunosuppressive potential. Transcriptional regulatory network (TRN) analysis identified transcription factors that were most likely to drive the phenotypes of SPP1+ and C1QC+ TAMs, including ELF2, JUND and RUNX1. Through cell-cell communication analysis, we discovered that SPP1+ TAMs interact with T cells via SPP1-CD44 signaling, while C1QC+ TAMs interact with NK cells through HLA-E-KLRC1 signaling, suggesting the potential involvement of these signaling pathways in TAM-mediated suppression of these cytotoxic lymphocytes. We prioritized ligand-receptor gene pairs, such as SEMA3D-NRP1 and LTBP3-ITGB5, which likely mediate the interaction between malignant sarcoma cells and SPP1+/C1QC+ TAMs based on their dominance across sarcoma subtypes and association with poorer clinical outcomes. On the other hand, our analysis revealed that sarcoma subtype-specific interactions between TAMs and malignant cells are common, highlighting the heterogeneity of signaling events across sarcoma subtypes.
Conclusion and Significance: Our study presents a comprehensive single-cell multi-omics characterization of pediatric sarcomas and sheds light on its tumor microenvironment. By identifying unique markers for immunosuppressive TAM subpopulations and elucidating intercellular interactions promoting tumor development, this study proposes potential therapeutic targets for sarcoma treatment based on the role of TAMs in sarcoma TME.
Citation Format: Zhan Zhang, Kyung Jin Ahn, Changya Chen, Rumeysa Biyik Sit, Hesham Mohei, Brian Lockhart, Malay Haldar, Kathrin Bernt, Vinodh Pillai, Kai Tan. Investigation of tumor-immune interactions in pediatric sarcomas using single-cell multi-omics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6883.