Cationic
liposomes enhanced the rate of transduction of target cells with retroviral vectors. The greatest effect was seen with the formulation
DC-Chol/DOPE, which gave a 20-fold increase in initial transduction rate. This allowed an efficiency of transduction after brief exposure of target cells to virus plus
liposome that could be achieved only after extensive exposure to virus alone. Enhancement with
DC-Chol/DOPE was optimal when stable virion-
liposome complexes were preformed. The transduction rate for complexed virus, as for virus used alone or with the polycation
Polybrene, showed first-order dependence on virus concentration. Cationic
liposomes, but not
Polybrene, were able to mediate envelope-independent transduction, but optimal efficiency required envelope-receptor interaction. When virus complexed with
DC-Chol/DOPE was used to transduce human
mesothelioma xenografts, transduction was enhanced four- to fivefold compared to that for virus alone. Since the efficacy of gene therapy is dependent on the number of cells modified, which is in turn dependent upon the balance between transduction and
biological clearance of the vector, the ability of cationic
liposomes to form stable complexes with retroviral vectors and enhance their rate of
infection is likely to be important for in vivo application.