Interactions in CSF1-driven Tenosynovial Giant Cell Tumors.

A major component of cells in Tenosynovial Giant Cell Tumor (TGCT) consists of bystander macrophages responding to CSF1 that is overproduced by a small number of neoplastic cells with a chromosomal translocation involving the CSF1 gene. An autocrine loop was postulated where the neoplastic cells would be stimulated through CSF1R expressed on their surface. Here we use single cell RNA sequencing to investigate cellular interactions in TGCT. A total of 18,788 single cells from three TGCT and two Giant Cell Tumor of Bone (GCTB) samples underwent singe cell RNAseq. The three TGCTs were additionally analyzed using long read RNA sequencing. Immunofluorescence and immunohistochemistry for a range of markers was used to validate and extend the scRNAseq findings. Two recurrent neoplastic cell populations were identified in TGCT that are highly similar to non-neoplastic synoviocytes. We identified GFPT2 as a marker that highlights the neoplastic cells in TCGT. We show that the neoplastic cells themselves do not express CSF1R. We identified overlapping features between the giant cells in TGCT and GCTB. The neoplastic cells in TGCT are highly similar non-neoplastic synoviocytes. The lack of CSF1R on the neoplastic cells indicates they may be unaffected by current therapies. High expression of GFPT2 in the neoplastic cells is associated with activation of the YAP1/TAZ pathway. In addition, we identified expression of the PDGF receptor in the neoplastic cells. These findings suggest two additional pathways to target in this tumor.