CD40 and glioblastoma: Although the screening of our glioblastoma cell lines and primary glioblastoma-initiating cell lines revealed only U87MG glioblastoma cells to be positive for CD40 membrane expression, which is in line with previously published data and might be due to a cell culture artifact (37), the expression data of the tumor tissue suggest that CD40 signaling might be relevant for a large subgroup of patients with high-grade glioma.