(A-B) Co-culture experiments of U87-FmC (A) or Gli36vIII-FmC (B) with engineered mMSC-TR-GFl or mMSC-TR-TK-GFl were performed as mentioned before in a 1:1 ratio and two days later GCV (10 μg/mL) was added to the cultures. Photomicrographs (original magnification, x4) show mMSC GFP-positive cells three days post GCV treatment. Plots show percentage of viability of modified mMSC-Fluc cells measured by Fluc signal at day three. In all panels, *, p < 0.05 versus controls. Bars, +SD. Abbreviations: mMSC, primary mouse mesenchymal stem cells; GCV, ganciclovir; Fluc, firefly luciferase; TK, Thymidine Kinase; TR, tumor necrosis factor apoptosis-inducing ligand; GFl, green fluorescent protein and Fluc fusion.