Western blot analysis confirmed IL-33 protein in the BTICs (Fig. 2a inset), and gene expression established a significant correlation between IL-33 in the BTIC and the matched primary GBM specimen from which they were derived (21 matched pairs; r = 0.60; p = 0.0043; see Supplementary Fig. 2a). This evidence concerns the gene IL33 and glioblastoma.