Repeated in vivo passaging cycles of human GBM xenografts in nude rats lead to loss of immunogenicity.

A. Left: In low generation xenografts, Allograft Inflammatory Factor-1 and Cathepsin S staining identified tumor-infiltrating microglia with predominantly intermediate and amoeboid morphology. Right: In high generation xenografts, immunopositive cells were less abundant. Box plots compare the numbers of AIF-1+ cells, or the area fractions occupied by Cat S+ cells per high power field (HPF, x400). Significant differences are denoted by asterisks (*** marks P<0.001, ** marks P<0.005). Circles represent outlier data points. B. Fold change comparison of transcript levels of selected human cytokines, chemokines and growth factors with relevance to immune responses in low- versus high generation xenografts. Of the panel of analysed transcripts in the array, only those with at least a three-fold change in levels between low and high generation in both patient xenografts are presented. C. Fold change of tumor-derived TGF-β2 transcripts in corresponding low and high generation xenografts. Mean ± SEM; three independent runs. Scale bars in A: 100 μm.