Ewing sarcoma single-cell transcriptome analysis reveals functionally impaired antigen-presenting cells.

Novel therapeutic strategies are urgently needed for high-risk Ewing sarcoma (EwS) patients and for the reduction of severe side-effects for all patients. Immunotherapy may fill this need, but its successful application has been hampered by a lack of knowledge on the composition and function of the EwS immune microenvironment. Here, we explore the immune microenvironment of EwS, by single-cell RNA sequencing of 18 EwS primary tissue samples. EwS is infiltrated by NK, T, and B cells, dendritic cells, and immunosuppressive macrophages. EwS-associated T cells show various degrees of dysfunction. The antigen-presenting cells found in EwS lack co-stimulatory gene-expression, implying functional impairment. Interaction analysis reveals a clear role for EwS tumor cells in turning the EwS immune microenvironment into an immunosuppressive niche. These results provide novel insights into the functional state of immune cells in the EwS tumor microenvironment and suggest mechanisms by which EwS tumor cells interact with, and shape, the immune microenvironment.