(A) Proliferation of GBM cells interacting with pericytes (PCC-GB) and pericytes interacting with GBM cells (GBC-PC), represented as cumulative population doubling (CPD), during different times of co-culture was measured and compared to proliferation of control GBM cells and pericytes. Results are mean + Standard Deviation of at least three different experiments, *p<0.05; **p<0.01. (B) Detection of death cell by blue-fluorescent reactive dye, of two representative populations of pericytes (PC1, PC2) compared to those same populations conditioned by GBM cells (GBC-PC1, GBC-PC2) (left panel). Quantification of dead cells percentage (right panel) from at least, four independent experiments. (C) GBM tumor growth in mice that were xenografted with GBM cells (GBM) compared with (D) xenografts of co-cultured PC and GBM cells (GBM+Pc) (scale bars, 100 μm). (E) Infiltration stream of GBM cells (GBM) together with a GFP+ Pericyte (Pc) in the perivascular space (scale bar, 25 μm). (F) Morphometric measurement reveals the average of tumor size in GBM grafted mice (GB) and GBM+Pc grafted mice (6 tumors / 5 grafted mice and 7 tumors / 5 grafted mice, respectively). (G) Representative detail of xenografts GBM+Pc shows proliferating GBM cells (GBM/Ki67+), which appear as intense RFP+ fluorescent spherical dividing cells, in which one of the sister cells is more intensely immunopositive (arrow) than the other (arrowhead) for both RFP (red) and Ki67 (green) (scale bar, 25 μm). (H) Proliferating cells (strong RFP+) in GBM xenografts and (I) GBM+Pc xenografts (scale bars, 50 μm). All results are shown using the U373 GBM line, 4 weeks after-graft, and are representative of at least four different experiments using U87 or U373 GBM lines independently. Control pericytes (0 tumors / 5 grafted mice (4weeks) and 0 tumors/ 5 grafted mice (11weeks)) not shown. (J) Relative quantification of number of dividing GBM cells in GBM+Pc and GB grafted mice. Results are mean+SD from at least four different experiments * p<0.05; *** p<0.0005. (K-P) IL-10 and TGF-β expression in control GBM xenografts (scale bars, 50 μm). (L, Q, S) Colocalization of the heterogeneous distribution of pericytes (GFP+, arrowheads) and (M, R, T) IL-10 and TGF-β expression (arrowheads) in GBM+Pc xenografts. (N, U) Merged pictures showing higher IL-10/ TGF-β expression in areas where grafted GBC-PC accumulate (arrows) (scale bars, 50 μm). (O, V) High-power confocal image (one micron-thick section) shows the colocalization of GFP and IL-10/ TGF-β in GBC-PC (arrows) (scale bars, 50 μm). Results are shown 4 weeks after-graft and are representative of at least, four independent experiments. (W) Quantification of IL-10 expression relative to total area of IL-10 immune-positive particules in GBC+Pc xenografts compared to GB control. (X) Relative quantification of TGF-β expression related to luminosity of TGFb immuno-processed sections in GBC+Pc xenografts compared to GB control. Results are mean+SD from at least four different experiments * p<0.05; *** p<0.0005.