Helper virus-free herpes simplex virus type 1 amplicon vectors for granulocyte-macrophage colony-stimulating factor-enhanced vaccination therapy for experimental glioma

Subcutaneous vaccination therapy with glioma cells, which are retrovirally transduced to secrete granulocyte-macrophage colony-stimulating factor (GM- CSF), has previously proven effective in C57BL/6 mice harboring intracerebr al GL261 gliomas. However, clinical ex vivo gene therapy for human gliomas would be difficult, as transgene delivery via retroviral vectors occurs onl y in dividing cells and ex vivo glioma cells have a low growth fraction. To circumvent this problem, a helper virus-free herpes simplex virus type 1 ( HSV-1) amplicon vector was used. When primary cultures of human glioblastom a cells were infected with HSV-1 amplicon vectors at an MOI of 1, more than 90% of both dividing and nondividing cells were transduced. When cells wer e infected with an amplicon vector, HSVGM, bearing the GM-CSF cDNA in the p resence of Polybrene, GM-CSF secretion into the medium during the first 24 hr after infection was 1026 ng/10(6) cells, whereas mock-infected cells did not secrete detectable GM-CSF. Subcutaneous vaccination of C57BL/6 mice wi th 5 X 10(5) irradiated HSVGM-transduced GL261 cells 7 days prior to intrac erebral implantation of 10(6) wild-type GL261 cells yielded 60% long-term s urvivors (> 80 days), similar to the 50% long-term survivors obtained by va ccination with retrovirally GM-CSF-transduced GL261 cells. In contrast, ani mals vaccinated with the same number of nontranduced GL261 cells or with GL 261 cells infected with helper virus-free packaged HSV-1 amplicon vectors c arrying no transgene showed only 10% long-term survivors. In conclusion, he lper virus-free HSV-1 amplicon vectors appear to be effective for cytokine- enhanced vaccination therapy of glioma, with the advantages that both divid ing and nondividing tumor cells can be infected, no viral proteins are expr essed, and these vectors are safe and compatible with clinical use.