Immunotherapy works amazingly well on some tumours, less on others. Brain cancers are among the hardest, because the blood-brain barrier physically prevents circulating immune cells from reaching the tumour. What is the point in boosting the immune response against cancer, if our soldiers cannot arrive on the spot? Finding a way into the brain is the biggest challenge. In a paper published on Nature, researchers engineered T cells, triggering their infiltration in a brain cancer called glioblastoma.