MSC delivery of MV to ALL cells. The top portion of the figure depicts live cell confocal microscopy showing the transfer (“handoff”) of GFP-expressing MV from a virus-loaded MSC (green) to an RFP-expressing Nalm-6 ALL cell. The ALL cells shift from red to yellow (and eventually green) fluorescence as more GFP-expressing virus enters within the RFP-expressing cell. Both cells will eventually undergo viral-mediated lysis. The bottom portion of the figure is a schematic representation of the cell MSC-ALL cell fusion and passage of GFP-expressing virus (open hexagon) into the RFP-expressing Nalm 6 ALL cell depicted by the red-orange-yellow-green color shift as the viral (green) fluorescence blends with and then overtakes the ALL cell (red) fluorescence. GFP, green fluorescent protein; RFP, red fluorescent protein. The top three panels have been adapted from Figure 4 in the article by Castleton et al that begins on page 1327.