Figure 1.

Effect of plasmid size on electrotransfer toxicity and efficacy. Adipose tissue-derived mesenchymal stem cells (AT-MSCs) were analyzed by flow cytometry 24 hours after treatment. Equimass experiment (a–c): AT-MSCs were electrotransferred (eight pulses, 1,500 V/cm, 100 µs, 1 Hz) with 50 µg of plasmids of various sizes. Equimolar experiment (d–f): AT-MSCs were electrotransferred with ~6.7 pmol of plasmids of various sizes (equivalent to 50 µg of the 11.4 kbp plasmid pCAGMKOSiE). In panels b and e, the open circles represent the percentage of treated cells expressing green fluorescent protein (GFP) and the filled triangles represent the percentage of surviving cells expressing GFP. In panels c and f, the dotted line represent the background fluorescence intensity of the controls. Data are representative of 4–10 independent experiments. The survival, percentage of transfection, and expression per cell are inversely correlated to the plasmid size in both equimolar and equimass experiments (P < 0.001, Kendall's rank correlation).