Comparison of lipid-mediated and adenoviral gene transfer in human monocyte-derived macrophages and COS-7 cells

Lipid-mediated transfection was compared to adenoviral-mediated gene transfer in COS-7 cells as well as human monocyte-derived macrophages (HMDM). For this purpose, we monitored enhanced green fluorescent protein (EGFP) expression by fluorescence microscopy and quantified gene transfer by competitive PCR. Transfection of COS-7 cells with a novel lipid formulation for DNA transfer was highly effective in COS-7 cells. On average, 30% of the cells were fluorescent 48 h after transfection. In HMDM, the same formulation resulted in the expression of EGFP in less than 0.5% of cells. We measured plasmid DNA by quantitative PCR in lipid-transfected macrophages and found that each macrophage contained on average 2 fg of plasmid DNA 24 h after transfection, that is, more than 400 molecules of plasmid DNA entered each cell. Despite the high level of reporter DNA in lipid transfected cells, expression of the fluorescent protein was suppressed in more than 99.5% of the macrophages. We also used adenoviral gene transfer to introduce the foreign DNA into both COS-7 cells and HMDM. Even though the multiplicity of infection was less than 30, expression of EGFP was observed in nearly all COS-7 cells and in more than 80% of HMDM 48 h after transfection. Despite major advances in the field of lipid-mediated transfection of HMDM, the lipid formulations that are available commercially cannot compete with the efficiency of adenoviral gene transfer.