Single-cell RNA-seq reveals identity and heterogeneity of malignant osteoblast cells and TME in osteosarcoma

Osteosarcoma (OS) has high heterogeneity and poor prognosis. In order to explore the molecular mechanism of OS and the tumor micro-environment (TME) on OS, we employed single-cell RNA-sequencing (scRNA-seq) on 110,745 individual cells from OS primary lesion, recurrent focal and metastatic tissues. We identified 5 main malignant subpopulations of OS cells, 3 clusters of osteoclast(OC) and 2 types of cancer-associated fibroblasts (CAFs). Further we found that the progenitor OC and, antigen presenting CAF (apCAF) were lower in lung metastatic and recurrent tumor tissues than in primary tumor tissue. M2-like macrophages were predominant in the TME myeloid cells. Inactivation state of tumor-infiltrating T cells, mainly the CD4-/CD8-T and Treg cells, existed in lung metastatic tissues. T-cell immunoreceptor with Ig and ITIM domains (TIGIT) expressed in 11 samples. We then blocked TIGIT which significantly enhancd the cytotoxic effects of primary T cells on OS cell lines. Our report represents the first use of scRNA-seq for the transcriptomic profiling of OS cells. Thus, the findings in this study will serve as a valuable resource for deciphering the intra-tumoral heterogeneity in OS and provide potential therapeutic strategies for OS in clinic.