AN IMPROVED RETROVIRAL VECTOR ENCODING THE HERPES-SIMPLEX VIRUS THYMIDINE KINASE GENE INCREASES ANTITUMOR EFFICACY IN-VIVO

Brain tumors have been treated clinically by intratumoral injection of cells that produce retroviral vectors encoding the herpes simplex vir us thymidine kinase (HSV-TK) gene followed by systemic administration of the antiviral drug ganciclovir. In vitro and in vivo comparisons of two different HSV-TK vector producer clones, which were made using st andard transfection and transinfection techniques, were conducted. The two clones, PA317/G1TkSvNa.53 (TK.53) and PA317/C1Tk1SvNa.7 (TK1.7), both used in clinical trials, differ with respect to sequences 3' to t he HSV-TK stop codon. The retroviral construct used to generate the TK .53 vector producer cell clone contains an open reading frame encoding a portion of the herpes simplex virus glycoprotein H (gH), a potentia l polyadenylation site and a putative splice site in this region. Thes e sequences were removed from the retroviral construct used to create the TK1.7 vector producer cell clone. Supernatants obtained from TK1.7 vector producer cells had 100- to 1000-fold higher titers (G418 or HA T) than did corresponding supernatants from TK.53 vector producer cell s. A murine subcutaneous tumor model was used to assess transduction e fficiency and antitumor activity of each vector producer cell clone. I n vivo tumor cell transduction was 13- to 18-fold more efficient with TK1.7 cells as compared with TK.53 cells at equivalent doses. Complete tumor ablation was achieved using a 10-fold lower dose of TK1.7 cells as compared with TK.53 cells. These results suggest that TK1.7 cells combined with ganciclovir may provide a more potent antitumor response in humans.