VACV expressing BMP-4 facilitates differentiation of GBM CSCs. A) Schematic representation of the two viruses used in the study. GLV-1h189 is the parental virus with insertions of a cDNA encoding a Renilla luciferase and GFP fusion in the F14.5 L locus, a lac Z cDNA in the J2R (thymidine kinase) locus and a turboRFP (tRFP) cDNA in the A56R locus. To construct GLV-1h285, a cDNA encoding BMP-4 was used to replace the lacZ cDNA. The promoters are indicated in front of the boxes representing the cDNAs. B) Infection of GBM CSC spheroids with the two viruses. Appearance of differentiated, adherent cells is evident upon GLV-1h285 infection (bottom left) whereas spheroids remain intact upon GLV-1h189 infection (top right) at 9 dpi (Magnification 4X). C) BMP-4 generated by GLV-1h285 has a distinct bystander effect. BMP-4 produced from GLV-1h285-infected spheroids (glowing green or red) differentiates the neighboring spheroids resulting in adherent cell clusters at 9 dpi (Magnification 10X).