Retroviral vectors are expected to be one of the most valuable viruses for gene delivery applications. Glycoproteins displaying on the retroviral surface are known to have critical functions for viral infection. These functions include the specific binding between viruses and cells and triggering the pH-dependent endosomal membrane fusion. Many attempts have been made to modify virus surface glycoproteins by inserting targeting molecules to enhance the interaction between the viruses and the cells. The major challenge has been that the retroviruses with the modified glycoproteins usually have lower activities at the stage of activation of endosomal membrane fusion because of such alterations.

We are developing a novel method of targeting retroviruses to a specific cell type. We have modified retrovirus glycoproteins by expressing the antibodies and fusogenic proteins (fusogen) as two separate molecules on the surface of the retroviruses. The specific targeting is determined by the antibody, and the fusogen triggers the fusion activity. We have used the 293T/CD20 cell line as the B-cell targeting model. The CD20 antigen is a known B-cell surface marker. An anti-human CD20 antibody, which is currently being used in the treatment of B cell lymphoma, is used as the targeting molecule on the virus surface, and a modified, cholesterol-independent form of Sindbus virus glycoprotein is used as a fusogen.

Our experiments have demonstrated that an engineered retroviral vector can be obtained by cotransfection of the virus packaging cell line, both binding protein (antibody or other proteins) and fusogen are necessary for this retroviral vector targeting strategy, different fusogens have different activity for retroviral infection, and efficient targeted infection was successfully achieved both in vitro and in vivo. Moreover, this targeting strategy can be readily extended to other cell types by choosing different binding proteins.