Lack of superinfection interference in retroviral vector producer cells

Vesicular stomatitis virus G protein (VSV-G)-pseudotyped retroviral vectors have become more feasible for clinical gene transfer protocols since stabl e tetracycline (tet)-regulated packaging cell lines have become available. Here, we analyzed superinfection interference in VSV-G-pseudotyped and clas sic amphotropic packaging cell lines. No superinfection interference was ob served in VSV-G-pseudotyped packaging cell lines. Thus, integrated retrovir al vector genomes accumulated during culture. Similar results were obtained with the amphotropic packaging cells, but to a lesser degree. In addition, VSV-G packaging cells were susceptible to infection with vector particles devoid of envelope proteins, which are produced by these cells in high tite rs when VSV-G expression is suppressed by tetracycline. For both packaging systems, superinfection could be blocked by azidothymidine (AZT). With rega rd to safety, this study suggests that in clinical protocols amphotropic pr oducer clones should be tested for superinfection interference and VSV-G pa ckaging cells should always be cultured in the presence of AZT.