Abstract 3133: Long-Term Labeling of Mesenchymal Stem Cells Using Quantum Dot Bioconjugates
Introduction: Quantum Dots (QDs) offer an alternative to organic dyes and fluorescent proteins to label and track transplanted mesenchymal stem cells (MSCs) in vitro and in vivo. These luminescent nanoparticles are resistant to chemical and metabolic degradation and have long term photostability. However, the effects of QDs on MSC proliferation and differentiation are unknown. To our knowledge this is the first report to assess the cytotoxicity of in vitro QD labeling in MSCs.
Methods: MSCs were isolated from long bones of 6 wk old rats and replated twice after reaching 80% confluency. MSC cultures were treated with No-QDs (Control), 8.5 μg/ml (LC) or 34 μg/ml (HC) QD Q-tracker 605 at 37°C for 1 hour. Measurements to evaluate MSC viability were recorded at 24, 72 and 120 hrs post treatment. MSC assessment included:
intracellular QD distribution,
MSC survival and identification of the apoptotic cell population (annexin assay),
single strand DNA (ssDNA) breaks (comet assay), and 4) levels of MCP-1, IL-1β, IL-6 and TNFα.
Results: A dose dependent effect was measured with increased yield in QD labeled MSCs for HC-MSCs vs. LC-MSCs (90% vs. 36%). HC-MSC proliferation decreased to 75% of Control and ssDNA breaks increased by 60% in HC-MSCs vs. Control at 120 hrs. Yet, approximately 90% of QD labeled MSCs (LC and HC) were annexin negative at 24 hrs and intracellular QDs were visible in both groups at 120 hrs. A 30% increase in MCP-1 and a two fold increase in IL-6, compared to Control were measured in both treatment groups at 24 hrs. No change in IL-1β and TNF-α was measured at either QD concentration.
Conclusion: QDs are effective for long-term MSC labeling applications when used at the recommended dose. The results suggest that QD treated MSCs should be transplanted within 24 hrs of labeling and not allowed to expand in culture or frozen for later use. Due to the ease of use, high yield and high survival rate of QD labeled MSCs we anticipate using QD labeled MSCs to monitor donor MSC engraftment, survival and differentiation in a rodent cardiac injury model in vivo.