To test whether this is an artifact due to medium-related conditions or a problem of established cell lines in general, the glioma-initiating cells S24, T1, T269, T325, ZH305, ZH161, WJ, KNG002, MM, and PJ (22) were also tested for CD40 expression by flow cytometry but were all negative (data not shown). This evidence concerns the gene CD40 and central nervous system cancer.