Complexation of retroviruses with charged polymers enhances gene transfer by increasing the rate that viruses are delivered to cells

Background We have previously found that retrovirus transduction is enhanced when an anionic polymer (chondroitin sulfate C) is added to virus stocks that contain an equal weight concentration of a cationic polymer (Polybrene). This observation was unexpected given that previous work has shown that cationic polymers enhance transduction while anionic polymers have the opposite effect. Methods Using model recombinant retroviruses and lentiviruses that encode for the Escherichia coli lacZ gene and quantitative assays of virus adsorption and transduction, we examined the mechanism of enhancement. Results We found that addition of oppositely charged polymers (Polybrene and chondroitin sulfate C) to virus stocks enhanced gene transfer by increasing the flux of active viruses to the cells. Virus-polymer complexes formed that did not reduce the stability of the viruses, yet were large enough to sediment, delivering the viruses to the cells more rapidly than by simple diffusion. The size of the complexes, the rate of sedimentation, and the levels of gene transfer increased with increasing concentrations of polymers. The degree to which transduction was enhanced ranged from 2- to nearly 40-fold, and varied depending on the type of cells and viruses used. Interestingly, we found that association of the viruses with the polymer complexes did not significantly hinder their ability to complete post-binding steps of transduction. Conclusions Complexation of retroviruses with charged polymers significantly improves the efficiency of ex vivo gene transfer by increasing the number of active viruses that reach the cells. Copyright (C) 2004 John Wiley Sons, Ltd.