TGFß inhibition during radiation therapy enhances immune cell infiltration and decreases metastases in a novel humanized mouse model Ewing sarcoma.

Ewing sarcoma is an aggressive cancer most commonly diagnosed in adolescents and young adults. Various mechanisms of TGFß inhibition are being tested in clinical trials for patients with relapsed Ewing sarcoma. However, the functional impact of TGFß inhibition on the Ewing tumor microenvironment remains largely unstudied given the historical lack of immunocompetent preclinical models of Ewing sarcoma. Here, we use single cell RNAseq analysis of human Ewing tumors to demonstrate that immune cells are the largest source of TGFß production in the human Ewing tumor microenvironment. We develop and utilize a humanized mouse model of Ewing sarcoma to study the effect of TGFß inhibition on the Ewing tumor immune microenvironment both at baseline and during radiation therapy, a treatment that enhances TGFß activation and is often used to treat patients with aggressive Ewing sarcoma. Finally, we utilize a bivalent ligand TGFß TRAP and demonstrate that, in combination with radiation, TGFß inhibition both increases immune cell infiltration in Ewing tumors and decreases lung metastatic burden. Overall design: In this study, tumor specimens were obtained from two patients with Ewing sarcoma. Dissociated single cell suspensions were subjected to 5'-based single-cell RNA sequencing using 10X Genomics.