The observation that subcutaneous injection of the Ad-VEGF+BMP-6 construct without the rMSCs did not result in any appreciable bone formation, as has been reported previously by others [6, 12, 14], suggests that the administration of the virus did not infect the endogenous cells in the host or that the rate of infection of host cells was insufficient to lead to bone formation in vivo, in the subcutaneous sites. This evidence concerns the gene BMP6 and infection.