Recombinant retroviruses are by far the most frequently used vehicle in clinical gene therapy. No serious side-effects have been reported so far in clinical gene therapy trials using recombinant retroviral systems. Low titers of recombinant retroviruses, however, have limited the usefulness of recombinant retroviruses. To improve the efficiency of retrovirus-mediated gene transfer, we previously introduced the polyomavirus early region into amphotropic PA317 cells and established a modified retroviral packaging cell line, PAMP51. We demonstrate here that recombinant retroviruses produced by PAMP51-derived retroviral producing cells have approximately 10-fold higher titers compared with those produced by conventional PA317-derived retroviral producing cells. Importantly, recombinant retroviruses produced by PAMP-derived retroviral producing cells could infect hepatocellular carcinoma cells much more efficiently and could induce much stronger expression of a lacZ reporter gene in HCC cells compared with those produced by PA317-derived ones. These results indicate that recombinant retroviruses prepared from PAMP51-derived retroviral producing cells are much more useful than those prepared from PA317-derived ones and that the use of PAMP51 retroviral packaging cells may open up new avenues for the treatment of various types of cancer including hepatocellular carcinoma.

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