Dynamic single‐cell sequencing unveils the tumor microenvironment evolution of gastric cancer abdominal wall metastases during radiotherapy

Although the combination of immunotherapy and radiotherapy (RT) for the treatment of malignant tumors has shown rapid development, the insight of how RT remodels the tumor microenvironment to prime antitumor immunity involves a complex interplay of cell types and signaling pathways, much of which remains to be elucidated. Four tumor samples were collected from the same abdominal wall metastasis site of the patient with gastric cancer at baseline and during fractionated RT for single-cell RNA and T-cell receptor sequencing. The Seurat analysis pipeline and immune receptor analysis were used to characterize the gastric cancer metastasis ecosystem and investigated its dynamic changes of cell proportion, cell functional profiles and cell-to-cell communication during RT. Immunohistochemical and immunofluorescent staining and bulk RNA sequencing were applied to validate the key results. We found tumor cells upregulated immune checkpoint genes in response to RT. The infiltration and clonal expansion of T lymphocytes declined within tumors undergoing irradiation. Moreover, RT led to the accumulation of proinflammatory macrophages and natural killer T cells with enhanced cytotoxic gene expression signature. In addition, subclusters of dendritic cells and endothelial cells showed decrease in the expression of antigen present features in post-RT samples. More ECM component secreted by myofibroblasts during RT. These findings indicate that RT induced the dynamics of the immune response that should be taken into consideration when designing and clinically implementing innovative multimodal cancer treatment regimens of different RT and immunotherapy approaches.