The effect of cationic liposome pretreatment and centrifugation on retrovirus-mediated gene transfer

Pretreatment of retroviral supernatants with the cationic liposomes DOTMA-DOPE (Lipofectin), DC-Chol-DOPE and DOSPA-DOPE (Lipofectamine) was found to enhance static transductions of TF-1 target cells. The relative effectiveness at increasing transduction efficiencies (TE) was: DOSPA > DC-Chol > DOTMA, resulting in average increases over nontreated controls of 11.9-, 6.2- and 1.2-fold, respectively. This pretreatment was found to be synergistic when combined with centrifugation, having the same order of effectiveness, and resulting in 57-, 35- and 27-fold increases over nontreated controls. For Lipofectamine and DC-Chol-DOPE liposomes, the combined approach yielded 2.2- and 1.3-fold increases over untreated centrifuged samples. Individual colonies picked from colony-forming unit granulocyte-macrophage assays of infected CD34+ cells were screened for the presence of the transgene by polymerase chain reaction (PCR). Colonies from cells infected using centrifugation were positive 27% of the time, while the combined approach had positive colonies 31 and 50% of the time for DC-Chol and Lipofectamine, respectively. The addition of protamine sulfate to the liposome-supernatant mixture during pretreatment was found to be inhibitory. With increasing centrifugal force, the TE of cells infected with Lipofectamine pretreated and untreated supernatants increased proportionally. However, the TE of the cells infected with the pretreated supernatants was significantly higher than the TE of the cells infected with untreated supernatants at all points examined. The increase in TE associated with liposomal pretreatment of retroviral supernatants was not shown to be attributed to a nonreceptor-mediated pathway for viral entry into the cell.