Background: The tumor microenvironment (TME) has been shown to strongly influence treatment outcome for cancer patients in various indications and to influence the overall survival. However, the cells forming the TME in gastric cancer have not been extensively characterized.Results: We combine bulk and single-cell RNA sequencing from tumors and matched normal tissue of 24 treatment-naïve GC patients to better understand which cell types and transcriptional programs are associated with malignant transformation of the stomach. Clustering 96,623 cells of non-epithelial origin reveals 81 well-defined TME cell types. We find that activated fibroblasts and endothelial cells are most prominently overrepresented in tumors. Intercellular network reconstruction and survival analysis of an independent cohort imply the importance of these cell types together with immunosuppressive myeloid cell subsets and regulatory T cells in establishing an immunosuppressive microenvironment that correlates with worsened prognosis and lack of response in anti-PD1-treated patients. In contrast, we find a subset of IFNγ activated T cells and HLA-II expressing macrophages that are linked to treatment response and increased overall survival.Conclusions: Our gastric cancer single-cell TME compendium together with the matched bulk transcriptome data provides a unique resource for the identification of new potential biomarkers for patient stratification. This study helps further to elucidate the mechanism of gastric cancer and provides insights for therapy.

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Background: Immunotherapy brings new hope to patients with advanced gastric cancer. However, liver metastases can reduce the efficacy of immunotherapy in patients. Tumor-associated macrophages (TAMs) may be the cause of this reduction in efficacy. SPP1 + TAMs are considered to have immunosuppressive properties. We aimed to investigate the involvement of SPP1 + TAMs in the metastasis of gastric cancer. Methods: The single-cell transcriptome was combined with batched BULK datasets for analysis. Animal models were used to verify the analysis results. Results: We reveal the interaction of SPP1 + TAMs with CD8 + exhausted T cells in metastatic cancer. Among these interactions, GDF15-TGFBR2 may play a key immunosuppressive role. We constructed an LR score to quantify interactions based on ligands and receptors. The LR score is highly correlated with various immune features and clinical molecular subtypes. The LR score may also guide the prediction of the efficacy of immunotherapy and prognosis. Conclusions: The crosstalk between SPP1 + TAMs and CD8 + exhausted T cells plays a key immunosuppressive role in the gastric metastatic cancer microenvironment. Graphical

Accumulating evidence has demonstrated that N6-methyladenosine (m6A) plays important roles in various cancers, making it essential to profile m6A modifications at a transcriptome-wide scale in colorectal cancer (CRC). In the present study, we performed high-throughput sequencing to determine the m6A methylome in CRC. We obtained 6 pairs of CRC samples and tumor-adjacent normal tissues from Peking University People’s Hospital. We used MeRIP-seq to determine that compared to the tumor-adjacent normal tissues, the CRC samples had 1343 dysregulated m6A peaks, and 625 m6A peaks were significantly upregulated and 718 m6A peaks were significantly downregulated. Genes with altered m6A peaks play critical roles in regulating glucose metabolism, RNA metabolism and cancer stem cells. Furthermore, we identified 297 hypermethylated m6A peaks and 328 hypomethylated m6A peaks in mRNAs through conjoint analyses of MeRIP-seq and RNA-seq data. After analyzing these genes with differentially methylated m6A peaks and synchronously differential expression, we identified four genes (WDR72, SPTBN2, MORC2 and PARM1) that were associated with prognosis of colorectal cancer patients by searching The Cancer Genome Atlas (TCGA). Our study suggests that m6A modifications play important roles in tumor progression and survival of CRC patients. The results also indicate that modulating m6A modifications may represent an alternative strategy to predict the survival of cancer patients and interfere with tumor progression in the future.