(235g) Rapid Modification of Retrovirus Surfaces for Targeted Gene Delivery

Retroviral-mediated gene transfer is a promising approach for the treatment of inherited genetic disorders, complex genetic disorders, and infectious diseases. Unfortunately, the use of retroviruses in the clinic has met with limited success, in part because it has proven difficult to control their tropism; that is, to ensure that retroviruses transduce only the targeted cell type and no others. To address this limitation, we have begun to develop a method for rapidly modifying the surface properties of retroviruses that uses bioconjugates that are composed of a poly (ethylene glycol) (PEG) chain and a cell-targeting functional group. These constructs, when mixed with a virus stock, rapidly assemble onto the surfaces of the particles. We used biotin as a model cell-targeting group to evaluate the ability of these constructs to modify a model replication-incompetent amphotropic retrovirus that encoded lacZ. We found that in less than 2 hours, the number of constructs that were associated with the particles reached a maximum. Even though the constructs were not covalently bound to the viruses, less than half dissociated from the viruses after 9 hours of incubation at 37 degC in medium that contained 10% fetal bovine serum. 7-fold more viruses modified with biotin conjugates bound to streptavidin coated plates than unmodified viruses. Importantly, virus titer experiments showed that the conjugates did not reduce the ability of the viruses to transduce cells. Lastly, we examined the ability of modified viruses to bind to cells that expressed the targeted receptor. The implications of our findings for the use of retroviruses in gene therapy protocols will be discussed.