Experimental gene therapy against subcutaneously implanted glioma with a herpes simplex virus-defective vector expressing interferon-gamma

We investigated the feasibility of local treatment or tumor vaccination wit h a herpes simplex virus (HSV) type 1-defective vector. The vector was engi neered to express murine interferon-gamma (IFN-gamma) for experimental gene therapy against mouse glioma Rous sarcoma virus (RSV). The murine IFN-gamm a gene was driven by the cytomegalovirus promoter. The helper virus (tsk) w as thermosensitive; consequently, this vector could only proliferate at 31 degrees C. A high level of murine IFN-gamma expression was confirmed in vit ro and in vivo by immunohistochemistry using anti-mouse IFN-gamma monoclona l antibody. This engineered vector (dvHSV/MuIFN-gamma) inhibited the prolif eration of mouse glioma RSV cells in vitro, and an intratumoral (i.t.) loca l injection of the vector caused i.t, necrosis in vivo. The immunological e ffect of dvHSV/MuIFN-gamma was also examined in a mouse glioma RSV cell imp lantation model. A subcutaneous (s.c.) implant of 1 x 10(6) mouse glioma RS V cells after treatment with dvHSV/MuIFN-gamma was rejected. However, the i mplant after treatment with an engineered HSV-defective vector containing a n antisense nucleotide sequence of the murine IFN-gamma gene was not reject ed. In addition, in another group of mice in which RSV cells treated with d vHSV/MuIFN-gamma were implanted into a femoral (s.c.) region and nontreated RSV cells were implanted into a contralateral femoral (s.c.) region, the i mplanted RSV cells were rejected. The rejection of the implanted mouse glio ma RSV was blocked by anti-asialo GM1, which was known to inhibit natural k iller cell activity. These results revealed that the HSV-defective vector c ould realize a high efficiency of transfection to glioma cells through shor t-time treatment, and that the IFN-gamma gene transferred to the cells had the effect of tumor vaccination, which was suggested be related to natural killer cells. In conclusion, dvHSV/MuIFN-gamma may be useful for the gene t herapy of malignant glioma through either i.t. local injection or a practic al tumor vaccination with ex vivo gene transfer.