Brain tumor cells with a certain common mutation reprogram invading immune cells. This leads to the paralysis of the body’s immune defense against the tumor in the brain. Researchers from Heidelberg, Mannheim and Freiburg discovered this mechanism, and at the same time, identified a way of reactivating the paralyzed immune system to fight the tumor. These results confirm that therapeutic vaccines or immunotherapies are more effective against brain tumors if active substances are simultaneously used to promote the suppressed immune system.