Our finding that TGFβ inhibition during radiotherapy significantly increases the total number of hu-CD34+ cells infiltrating Ewing sarcomas suggests that the immune microenvironment of Ewing sarcoma is modifiable and that combining TGFβ inhibition with radiotherapy could be utilized as a tool to enhance total immune cell infiltration in human Ewing sarcomas. Here, TGFB1 is linked to Ewing sarcoma.