Retrovirus targeting by tropism restriction to melanoma cells

Targeted vectors will be necessary for many gene therapy applications. To t arget retroviruses to melanomas, we fused a single-chain variable fragment antibody (scFv) directed against the surface glycoprotein high-molecular-we ight melanoma-associated antigen (HMW-MAA) to the amphotropic murine leukem ia virus envelope. A proline-rich hinge and matrix metalloprotease (MMP) cl eavage site linked the two proteins. The modified viruses bound only to HMW -MAA-expressing cells, as inclusion of the proline-rich hinge prevented vir al binding to the amphotropic viral receptor. Following attachment to HMW-M AA, MMP cleavage of the envelope at the melanoma cell surface removed the s cFv and proline-rich hinge, allowing infection. Complexing of targeted retr oviruses with 2,3-dioleoyloxy-N-[2(spermine-carboxamido)ethyl]N,N-dimethyl- 1-propanaminium trifluoroacetate-dioleoyl phosphatidylethanolamine liposome s greatly increased their efficiency without affecting their target cell sp ecificity. In a cell mixture, 40% of HMW-MAA-positive cells but less than 0 .01% of HMW-MAA-negative cells were infected. This approach can therefore p roduce efficient, targeted retroviruses suitable for in vivo gene delivery and should allow specific gene delivery to many human cell types by inclusi on of different scFv and protease combinations.