Integrated analysis of single-cell and bulk RNA sequencing data reveals an immunostimulatory microenvironment in tumor thrombus of osteosarcoma

Tumor thrombus of bone sarcomas represents a unique reservoir for various types of cancer and immune cells, however, the investigation of tumor thrombus at a single-cell level is very limited. And it is still an open question to identify the thrombus-specific tumor microenvironment that is associated with the tumor-adaptive immune response. Here, by analyzing bulk tissue and single-cell level transcriptome from the paired thrombus and primary tumor samples of osteosarcoma (OS) patients, we define the immunostimulatory microenvironment in tumor thrombus of OS with a higher proportion of tumor-associated macrophages with M1-like states (TAM-M1) and TAM-M1 with high expression of CCL4. OS tumor thrombus is found to have upregulated IFN-gamma and TGF-beta signalings that are related to immune surveillance of circulating tumor cells in blood circulation. Further multiplexed immunofluorescence staining of the CD3/CD4/CD8A/CD68/CCL4 markers validates the immune-activated state in the tumor thrombus samples. Our study first reports the transcriptome differences at a single-cell level between tumor thrombus and primary tumor in sarcoma.

Automated summary

By analyzing the transcriptome at both bulk tissue and single-cell levels, our study reveals the immunostimulatory microenvironment in tumor thrombus of osteosarcoma, characterized by a higher proportion of TAM-M1 with high expression of CCL4. Moreover, we find that upregulated IFN-gamma and TGF-beta signaling in tumor thrombus are related to immune surveillance of circulating tumor cells. This study provides insights into the unique tumor microenvironment of bone sarcoma thrombus and its association with immune response.