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

Abstract

We investigated the feasibility of local treatment or tumor vaccination with a herpes simplex virus (HSV) type 1-defective vector. The vector was engineered to express murine interferon-γ (IFN-γ) for experimental gene therapy against mouse glioma Rous sarcoma virus (RSV). The murine IFN-γ gene was driven by the cytomegalovirus promoter. The helper virus (tsk) was thermosensitive; consequently, this vector could only proliferate at 31°C. A high level of murine IFN-γ expression was confirmed in vitro and in vivo by immunohistochemistry using anti-mouse IFN-γ monoclonal antibody. This engineered vector (dvHSV/MuIFN-γ) inhibited the proliferation of mouse glioma RSV cells in vitro, and an intratumoral (i.t.) local injection of the vector caused i.t. necrosis in vivo. The immunological effect of dvHSV/MuIFN-γ was also examined in a mouse glioma RSV cell implantation model. A subcutaneous (s.c.) implant of 1 × 10⁶ mouse glioma RSV cells after treatment with dvHSV/MuIFN-γ was rejected. However, the implant after treatment with an engineered HSV-defective vector containing an antisense nucleotide sequence of the murine IFN-γ gene was not rejected. In addition, in another group of mice in which RSV cells treated with dvHSV/MuIFN-γ were implanted into a femoral (s.c.) region and nontreated RSV cells were implanted into a contralateral femoral (s.c.) region, the implanted RSV cells were rejected. The rejection of the implanted mouse glioma RSV was blocked by anti-asialo GM1, which was known to inhibit natural killer cell activity. These results revealed that the HSV-defective vector could realize a high efficiency of transfection to glioma cells through short-time treatment, and that the IFN-γ gene transferred to the cells had the effect of tumor vaccination, which was suggested be related to natural killer cells. In conclusion, dvHSV/MuIFN-γ may be useful for the gene therapy of malignant glioma through either i.t. local injection or a practical tumor vaccination with ex vivo gene transfer.