Human breast tumor-associated endothelial cells were purchased from Cell Biologics (Cat No HC-6020; Chicago, IL) and seeded in H1168 Complete Human Endothelial Cell Medium (Cell Biologics) in multiwell plates 1 day before transfection. The transfection was carried out with a modified mRNA (details on mRNA structure withheld due to confidentiality) by using the transfection reagents Prime-Fect (RJH Biosciences), LipofectamineTM 3000 (ThermoFisher) and other experimental reagents from the RJH Biosciences. The complexes were formulated at a reagent:nucleic acid ratio of 5:1 (w/w). After incubation of cells with the complexes for 2 days, the media were replaced, the cells were washed and recovered (by trypsin) for flow cytometry analysis. The mean percentage of cells positive for GFP expression was summarized below.