Updated project metadata. Glioblastoma is the most aggressive primary brain tumor with an unmet need for more effective therapies. Here we report that the combination of L19TNF, an antibody-cytokine fusion protein based on tumor necrosis factor that selectively localizes on the tumor neo-vasculature, with the alkylating agent lomustine, can induce tumor regression in orthotopic glioma-bearing mice and patients with recurrent glioblastoma. Mechanistically, this striking synergy crucially depended on T cells and involved activation of the tumor endothelium, tumor DNA damage, treatment-associated tumor necrosis, increased antigen presentation on MHC class I and tumor immune cell infiltration, as well as decreased tumor-associated immunosuppression. The clinical translation of this approach is ongoing, but already shows durable responses in the first recurrent glioblastoma patient cohort treated with L19TNF in combination with lomustine (NCT04573192).