Comprehensive analysis of the tumor immune microenvironment in gastric cancer and peritoneal metastasis based on single-cell RNA sequencing analysis.

The development and metastasis of gastric cancer are complex processes involving the TME (Tumor microenvironment) and the interactions between various cell types. Here, we investigated the molecular mechanisms and biological processes underlying gastric cancer and its metastasis using single cell RNA-sequencing (scRNA-seq) with the aim of identifying new targets and approaches for clinical treatment. R version 4.4.1 and the SeuratV5 package were used to process 20 scRNA-seq samples sourced from the GEO database. Highly variable genes were selected for GO (Gene Ontology), KEGG (Kyoto Encyclopedia of Genes and Genomes) and GSAV (Gene set variation analysis) enrichment analyses. CytoTRACE, CellChat, and Monocle3 analyses were conducted to investigate cell communication and pseudotemporal dynamics in the PM (Peritoneal Metastasis) and GC (Gastric Cancer) groups. Additionally, the prognostic significance of key genes was assessed by integrating data from the TCGA clinical database. A total of 2,626,594 peritoneal metastasis cells and 17,894 gastric cancer cells were identified, revealing 13 distinct cell clusters. Gene enrichment analyses identified high expression in several pathways (P53, Wnt and JAK-STAT3) in TAMs and mast cells. Cell communication was more robust in the GC group than the PM group, with TAMs (Tumor-associated Macrophages) and mast cells showing elevated expression of the CCL5-CCR1 ligand-receptor signaling axis in both groups. Pseudotemporal analysis demonstrated the differentiation potential of TAMs into mast cells, with APOC1, C1QB, FCN1, FTL, S100A9, CD1C, CD1E and FCER1A identified as the top eight genes driving this process. High expression levels of these genes, along with CCL5 and CCR1, were associated with poor long-term survival in cancer patients. scRNA-seq identified the intricate tumor immune microenvironment, highlighting the pivotal roles of TAMs and mast cells in gastric cancer peritoneal metastasis. The CCL5-CCR1 pathway emerged as a potential immune checkpoint, offering novel insights for future immunotherapeutic and targeted therapeutic strategies in the treatment of gastric cancer peritoneal metastasis.