Revealing the transcriptional heterogeneity of organ‐specific metastasis in human gastric cancer using single‐cell RNA Sequencing

Abstract

Background Deciphering intra‐ and inter‐tumoural heterogeneity is essential for understanding the biology of gastric cancer (GC) and its metastasis and identifying effective therapeutic targets. However, the characteristics of different organ‐tropism metastases of GC are largely unknown. Methods Ten fresh human tissue samples from six patients, including primary tumour and adjacent non‐tumoural samples and six metastases from different organs or tissues (liver, peritoneum, ovary, lymph node) were evaluated using single‐cell RNA sequencing. Validation experiments were performed using histological assays and bulk transcriptomic datasets. Results Malignant epithelial subclusters associated with invasion features, intraperitoneal metastasis propensity, epithelial–mesenchymal transition‐induced tumour stem cell phenotypes, or dormancy‐like characteristics were discovered. High expression of the first three subcluster‐associated genes displayed worse overall survival than those with low expression in a GC cohort containing 407 samples. Immune and stromal cells exhibited cellular heterogeneity and created a pro‐tumoural and immunosuppressive microenvironment. Furthermore, a 20‐gene signature of lymph node‐derived exhausted CD8+ T cells was acquired to forecast lymph node metastasis and validated in GC cohorts. Additionally, although anti‐NKG2A (KLRC1) antibody have not been used to treat GC patients even in clinical trials, we uncovered not only malignant tumour cells but one endothelial subcluster, mucosal‐associated invariant T cells, T cell‐like B cells, plasmacytoid dendritic cells, macrophages, monocytes, and neutrophils may contribute to HLA‐E‐KLRC1/KLRC2 interaction with cytotoxic/exhausted CD8+ T cells and/or natural killer (NK) cells, suggesting novel clinical therapeutic opportunities in GC. Additionally, our findings suggested that PD‐1 expression in CD8+ T cells might predict clinical responses to PD‐1 blockade therapy in GC. Conclusions This study provided insights into heterogeneous microenvironment of GC primary tumours and organ‐specific metastases and provide support for precise diagnosis and treatment.

Discovering Immune-Mediated Mechanisms of Gastric Carcinogenesis Through Single-Cell RNA Sequencing

“…Similarly, a large number of Tregs showed infiltration into the tumor tissue compared to the adjacent tissue. Along with all these findings, Jiang et al (2022) and Kumar et al (2022) confirmed that with tumor progression the tissue microenvironment changes from predominance of proinflammatory effectors to predominance of immunosuppressive Tregs (34,35). Qu et al (2022) identified a distinct Treg phenotype that is increased in tumor tissue compared to patientmatched blood and defined by enriched expression of the TNF receptor superfamily member 1B (TNFR2) (30).…”

“…This is because DCs are not always identified within the datasets, and if they are, they are generally represented at a low frequency. Jiang et al (2022) found the greatest population of DCs in metastatic lymph node derived tissue compared to primary tumor tissue (34). This is unsurprising since DCs typically reside in high frequency in the lymph node.…”

“…A study that examined the CTLs within a rare type of gastric cancer, hepatoid adenocarcinoma of the stomach, found the CTLs with an exhausted phenotype; therefore, NKT cells may be more capable of long-standing cytotoxic effector function (25). There was also an enrichment in exhausted CTLs in patients with metastatic compared to non-metastatic gastric cancer correlating with worse survival outcomes (34). Fu et al (2020) found there was decreased expression of the transcription factor IRF8 in cancer CTLs compared to normal tissue CTLs, thereby hinting that this method could be a new way to identify exhausted CTLs (20).…”

“…Prior to the scRNAseq studies, the macrophage types were identified with a protein marker, the scavenger receptor CD163, which is differentially enriched in M2s over M1s (69). However, in many scRNAseq studies looking specifically at the immune cells of gastric cancer tissue, the subsets of macrophages do not distinctly cluster based on M1/M2 polarization but fall into other discrete phenotypes where the same clusters do coexpress M1 and M2 markers (21,26,34,39,45,70). These results suggest that TAMs may be more diverse than previously thought.…”

“…Among the published scRNAseq gastric cancer works, it is apparent that they have undertaken various approaches to their studies. Most groups obtained primary gastric cancer tissues from patients to generate scRNAseq data (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35). Some utilized previously published primary tumor datasets for further analysis (36)(37)(38)(39)(40)(41)(42)(43).…”