The Effect of Lipid Antioxidant α-Tocopherol on Cell Viability and Electrofusion Yield of B16-F1 Cells In Vitro

Feasibility Study for the Use of Gene Electrotransfer and Cell Electrofusion as a Single-Step Technique for the Generation of Activated Cancer Cell Vaccines

Cell-based therapies hold great potential for cancer immunotherapy. This approach is based on manipulation of dendritic cells to activate immune system against specific cancer antigens. For the development of an effective cell vaccine platform, gene transfer, and cell fusion have been used for modification of dendritic or tumor cells to express immune (co)stimulatory signals and to load dendritic cells with tumor antigens. Both, gene transfer and cell fusion can be achieved by single technique, a cell membrane electroporation. The cell membrane exposed to external electric field becomes temporarily permeable, enabling introduction of genetic material, and also fusogenic, enabling the fusion of cells in the close contact. We tested the feasability of combining gene electrotransfer and electrofusion into a single-step technique and evaluated the effects of electroporation buffer, pulse parameters, and cell membrane fluidity for single or combined method of gene delivery or cell fusdion. We determined the percentage of fused cells expressing green fluorescence protein (GFP) in a murine cell model of melanoma B16F1, cell line used in our previous studies. Our results suggest that gene electrotransfer and cell electrofusion can be applied in a single step. The percentage of viable hybrid cells expressing GFP depends on electric pulse parameters and the composition of the electroporation buffer. Furthermore, our results suggest that cell membrane fluidity is not related to the efficiency of the gene electrotransfer and electrofusion. The protocol is compatible with microfluidic devices, however further optimization of electric pulse parameters and buffers is still needed.

The impact of impaired DNA mobility on gene electrotransfer efficiency: analysis in 3D model

Background

Gene electrotransfer is an established method that enables transfer of DNA into cells with electric pulses. Several studies analyzed and optimized different parameters of gene electrotransfer, however, one of main obstacles toward efficient electrotransfection in vivo is relatively poor DNA mobility in tissues. Our aim was to analyze the effect of impaired mobility on gene electrotransfer efficiency experimentally and theoretically. We applied electric pulses with different durations on plated cells, cells grown on collagen layer and cells embedded in collagen gel (3D model) and analyzed gene electrotransfer efficiency. In order to analyze the effect of impaired mobility on gene electrotransfer efficiency, we applied electric pulses with different durations on plated cells, cells grown on collagen layer and cells embedded in collagen gel (3D model) and analyzed gene electrotransfer efficiency.

Results

We obtained the highest transfection in plated cells, while transfection efficiency of embedded cells in 3D model was lowest, similarly as in in vivo. To further analyze DNA diffusion in 3D model, we applied DNA on top or injected it into 3D model and showed, that for the former gene electrotransfer efficiency was similarly as in in vivo. The experimental results are explained with theoretical analysis of DNA diffusion and electromobility.

Conclusion

We show, empirically and theoretically that DNA has impaired electromobility and especially diffusion in collagen environment, where the latter crucially limits electrotransfection. Our model enables optimization of gene electrotransfer in in vitro conditions.

Changes in the packing of bilayer lipids triggered by electroporation: real-time measurements on cells in suspension

Electropermeabilization of the cell membrane is a technique used to facilitate penetration of impermeant molecules into cells. Although there are studies regarding the mechanism of processes occurring after electropermeabilization, the relationship between electropermeabilization and associated phenomena (e.g. generation of reactive oxygen species, endocytosis, lipid peroxidation, etc.) is yet to be elucidated. This work aimed to get information on the changes in the packing of the bilayer lipids and their peroxidation induced by application of electroporation pulses. We used a specially designed system of electrodes which allowed performing electropermeabilization of cells in suspension simultaneously with time-dependent measurements of fluorescence and temperature. The kinetics of membrane packing and production of reactive oxygen species were studied using various conductivity buffers (0.01, 0.04 and 0.14 S/m) and different number of 1 kV/cm bipolar pulses (1-50). Two categories of effects were observed: a thermal effect, consisting in an increased bilayer disorder (a deeper penetration of water into the hydrophobic core), and a nonthermal effect, leading to a higher degree of lipids packing, the latter being attributed to a peroxidation process. An analysis of the permeabilization conditions in which one of these two processes predominates was performed.