Oncolytic Maraba virus MG1 mediates direct and natural killer cell-dependent lysis of Ewing sarcoma

Ewing sarcoma (EWS) is a rare cancer of the bone and soft tissue, most prevalent in children and young adults. Treatment of EWS has progressed relatively little in over 30 years. Survival rates for patients, particularly those with metastatic and/or relapsed disease, remain poor, highlighting the urgent need for innovative treatment options. We have explored the therapeutic potential of the oncolytic Maraba virus strain MG1. We show that MG1 undergoes productive replication and exerts direct oncolysis of established EWS cell lines, doxorubicin-resistant EWS cell lines and patient-derived Ewing sarcoma (PDES) cell cultures more recently established from tumours. In contrast, primary mesenchymal stem cells (the likely cell of origin of EWS) were resistant to MG1, with IFN-I being a major determinant of tumour cell selectivity. MG1 treated PBMC produced IFN-I and killed EWS cells in vitro, in a natural killer (NK) cell-dependent manner. The ability of MG1 to kill EWS cells directly and to stimulate NK cell cytotoxicity against this tumour suggests that Maraba virus MG1 may provide therapeutic benefit for EWS patients where the efficacy of conventional treatments is currently limited.