Retroviral Infection Is Limited by Brownian Motion

Abstract

Replication-defective retroviruses are frequently used as gene carriers for gene transfer into target cells. Here we show that the short half-lives of retroviruses limit the distance that they can effectively travel in solution by Brownian motion, and thus the possibility of successful gene transfer. This physicochemical limitation can be overcome, and effective contact between the retroviral gene carrier and the target cell can be obtained, by using net convective flow of retrovirus-containing medium through a layer of target cells. Using model cell lines (NIH-3T3 and CV-1), it was shown that gene transfer rates can be increased by more than an order of magnitude using the same concentration infection medium. High transduction rates could be obtained even in the absence of polycations, such as Polybrene, which heretofore have been required to achieve reasonable transduction rates. This development may play an important role in realizing human gene therapy. Retroviruses have short half-lives and therefore can only travel a limited distance by random Brownian motion in infection medium before deactivating. This distance is only a few hundred microns, and this constraint is shown to limit gene transfer rates. This limitation can be overcome by slow flow of the infection medium vertically through the target cell bed and gene transfer rates can be substantially increased.