EXPRESSION OF CHIMERIC ENVELOPE PROTEINS IN HELPER-CELL LINES AND INTEGRATION INTO MOLONEY MURINE LEUKEMIA-VIRUS PARTICLES

New retroviral constructs with a grafted specificity of infection coul d become useful gene delivery vehicles with applications in systemic g ene therapy. We have constructed retroviral vectors to target gene tra nsfer to human tumor cells. Chimeric envelope proteins have been expre ssed to obtain viral particles with a defined specificity of infection . Two tumor cell-specific recognition domains were cloned and fused wi th the viral envelope gene. A recognition domain specific for ErbB-2 e xpressing tumor cells was derived from a monoclonal antibody directed against the ErbB-2 receptor in the form of a single chain antibody dom ain (scFv-erbB-2). The receptor binding domain was derived from the he regulin gene (HRG70). This domain provides recognition specificity for ErbB-3 and ErbB-4 receptor expressing tumor cells. The recognition do mains were inserted at the amino terminal end into the MoMLV envelope gene. Helper cell lines were established which express the recombinant envelope protein genes, the gag and pol genes and packageable retrovi ral RNA. The analysis of the helper cell line revealed that the recomb inant ErbB-2 scFv-envelope protein was expressed, but not incorporated into viral particles. ThescFv-erbB-2-envelope protein was not inserte d into the cell membrane and the assembly of retroviral particles was not completed. In contrast, the HRG-70-envelope protein was expressed on the surface of the helper cells and incorporated into retroviral pa rticles. The HRG70-envelope protein, however, did not alter the host r ange of infection. Only cells expressing the ecotropic viral receptor could be infected.