Glioblastomas are malignant tumors of the central nervous system which lead to death within 1-2 years. Promising immunotherapeutic approaches failed to improve survival in glioblastomas. Although the reasons are not completely understood yet, it is assumed that the tumor environment is a barrier for immune cells. In the funded research project, we aim is to investigate the mechanism by which the inactivation of the immune system occurs, which cells are engaged in this process and how this inactivation can be prevented. We hope to gain detailed knowledge regarding the dynamic changes of the immune system in malignant brain tumors and identify potential targets for new immune therapies.