# Oncolytic Maraba Virus MG1 Mediates Direct and Natural Killer Cell-Dependent Lysis of Ewing Sarcoma

## TL;DR

The Maraba virus MG1 can directly destroy Ewing sarcoma cells and boost immune cell activity, offering a new treatment option for this aggressive cancer.

## Contribution

MG1's direct oncolytic effect and NK cell-dependent immune stimulation in Ewing sarcoma is newly demonstrated.

## Key findings

- MG1 directly kills Ewing sarcoma cell lines, including doxorubicin-resistant and patient-derived cultures.
- MG1 activates peripheral blood mononuclear cells and enhances natural killer cell-mediated destruction of Ewing sarcoma cells.
- Primary mesenchymal stem cells are resistant to MG1, with IFN-I playing a key role in tumor cell selectivity.

## Abstract

The five-year survival rates of Ewing sarcoma (EWS) patients, particularly those with metastatic and/or relapsed disease are poor and remain at less than 30%. This highlights a desperate need for new treatment approaches. The aim of this study was to investigate the efficacy of oncolytic Maraba virus strain, MG1, using in vitro models of EWS. Here, we demonstrate that MG1 exerts direct lytic effects on established EWS cell lines, doxorubicin resistant cell lines, spheroid cultures and primary patient-derived EWS cell cultures. We also explored the immune-stimulatory properties of MG1, where MG1 activated human healthy donor peripheral blood mononuclear cells and increased the immune-mediated destruction of EWS. These findings highlight the therapeutic potential of MG1 for EWS and warrant further investigation.

Background: Ewing sarcoma (EWS) is a rare cancer of the bone and soft tissue, most prevalent in children and young adults. The 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. Methods: Here, we have explored the therapeutic potential of the oncolytic Maraba virus strain MG1 using various in vitro models of EWS, including established cell lines, doxorubicin-resistant derivatives, spheroid cultures and primary patient-derived Ewing sarcoma cell cultures. We examined the direct oncolytic activity of MG1 and its ability to stimulate the immune-mediated killing of EWS by human healthy donor peripheral blood mononuclear cells. Results: 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 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. Conclusions: The ability of MG1 to kill EWS cells directly and stimulate NK cell cytotoxicity against this tumour suggests that MG1 may provide therapeutic benefit for EWS patients where the efficacy of conventional treatments is currently limited.