Nonviral gene delivery to mesenchymal stem cells using cationic liposomes for gene and cell therapy.

Mesenchymal stem cells (MSCs) hold a great promise for application in several therapies due to their unique biological characteristics. In order to harness their full potential in cell-or gene-based therapies it might be advantageous to enhance some of their features through gene delivery strategies. Accordingly, we are interested in developing an efficient and safe methodology to genetically engineer human bone marrow MSC (BM MSC), enhancing their therapeutic efficacy in Regenerative Medicine. The plasmid DNA delivery was optimized using a cationic liposome-based reagent. Transfection efficiencies ranged from approximately 2% to approximately 35%, resulting from using a Lipid/DNA ratio of 1.25 with a transgene expression of 7 days. Importantly, the number of plasmid copies in different cell passages was quantified for the first time and approximately 20,000 plasmid copies/cell were obtained independently of cell passage. As transfected MSC have shown high viabilities (>90%) and recoveries (>52%) while maintaining their multipotency, this might be an advantageous transfection strategy when the goal is to express a therapeutic gene in a safe and transient way.

A quantitative method to evaluate mesenchymal stem cell lipofection using real-time PCR.

Genetic modification of human mesenchymal stem cells (MSC) is a powerful tool to improve the therapeutic utility of these cells and to increase the knowledge on their regulation mechanisms. In this context, strong efforts have been made recently to develop efficient nonviral gene delivery systems. Although several studies addressed this question most of them use the end product of a reporter gene instead of the DNA uptake quantification to test the transfection efficiency. In this study, we established a method based on quantitative real-time PCR (RT-PCR) to determine the intracellular plasmid DNA copy number in human MSC after lipofection. The procedure requires neither specific cell lysis nor DNA purification. The influence of cell number on the RT-PCR sensitivity was evaluated. The method showed good reproducibility, high sensitivity, and a wide linear range of 75-2.5 x 106 plasmid DNA copies per cell. RT-PCR results were then compared with the percentage of transfected cells assessed by flow cytometry analysis, which showed that flow cytometry-based results are not always proportional to plasmid cellular uptake determined by RT-PCR. This work contributed for the establishment of a rapid quantitative assay to determine intracellular plasmid DNA in stem cells, which will be extremely beneficial for the optimization of gene delivery strategies.