Ewing sarcoma cell lines were provided by Dr. Timothy Triche Children's Hospital Los Angeles (CHLA, Los Angeles, CA) and the Children's Oncology Group (COG) cell bank (www.cogcell.org). HuVECs were obtained from Lonza (191027). MRC-5 cells were obtained from ATCC (CCL-171). Human bone marrow-derived mesenchymal stem cell (MSC) lines and hESC-derived neural crest stem cells were obtained as previously described (24 (link)). Identities were confirmed by short tandem repeat profiling. All cell lines were cultured in standard cell culture media, supplemented with 10% FBS (Atlas Biologicals, Inc., F-500-A) at 37°C in 5% CO2. Ewing sarcoma tumor specimens were acquired from the Vanderbilt University pathology archives. Approval from the Vanderbilt University Institutional Review Board was granted prior to tissue acquisition.