The research focuses on the development of a next-generation oncolytic virus for the treatment of glioblastoma, the most aggressive brain tumours. Oncolytic viruses are therapeutic viruses that replicate selectively in tumor cells. This causes lysis of the tumour cells, destroying the tumour. A promising technology, but the chance of unwanted immune responses is very high. In addition, the penetration of the virus to distant tumor cells is limited, making repeated treatment necessary. This research developes a technology to rid viruses of their immunogenic virus coat and to package the virus genome in an exosome. Exosomes are specific to the body and therefore invisible to the immune system, and exosomes can penetrate deeply into tissues.