Intracellular QD yield, retention and distribution in expanding MSC cultures. a. Flow cytometry results of QD positive MSCs in HC and LC groups at 24, 72 and 120 hrs post labeling. A dose-dependent effect is shown with increased HC vs. LC QD labeled MSCs detected at each time point (p < 0.05). b. Quantitative imaging results show a greater number of QD aggregates in the HC vs. LC MSCs at each time point (p < 0.05). The average number of intracellular QD aggregates increased from 24 to 72 hrs in both groups of MSCs (p < 0.05). No statistically significant changes in QD aggregates were measured from 72 – 120 hr. c. Representative confocal fluorescent images of LC and HC MSCs co-labeled with calcein (green) at 24 and 120 hrs. Each image represents a 1 μm thick optical slice establishing a peri-nuclear intracellular distribution of QDs. As the MSCs proliferated QDs remained bright and easy to detect. Scale bar 20 μm.