A new tool for DNA transfer to fish cell lines such as epithelioma papulosum cyprini (EPC) and rainbow
trout gonad (RTG2), has been optimized by testing commercially available polyethylenimine (PEI)
polymers as transfectant reagents. Deacylated 25 kDa PEI polymers were selected amongst the most
active and then low toxicity deacylated PEIs fractions around 15 kDa were obtained by gel filtration
chromatography to increase 3–4-fold their initial in vitro transfection efficiency. The EPC and plasmids
coding for reporter genes were first used to optimize variable values for best expression by transfection
with deacylated low toxicity PEI while both EPC/RTG2 and a plasmid coding for the glycoprotein G gene
of the fish pathogen, viral haemorrhagic septicemia virus (VHSV) were then used to demonstrate some of
their practical applications. Due to its relatively low price, defined chemical composition and availability,
low toxicity deacylated PEI might be used for numerous applications for all those studying fish cell
immunology in vitro as well as in vivo.