Prolonged survival of rats with intracranial C6 gliomas by treatment wit~ TGF-β antisense gene

Abstract

Using an intracranial rat C6 glioma model, we tested the hypothesis that gene modification ofglioma cells to block the expression of the immunosuppressive cytokine TGF-[3 (transforming growth factor (3) may enhance anti-tumor immune responses and thereby prolong survival of tumor-bearing animals. The cDNA for simian TGF-β2 was ligated in antisense orientation into the episomal plasmid mammalian expression vector pCEP-4. This TGF-β-antisense vector was transfected into C6 glioma cells by standard electroporation techniques. PCR was used to determine that the rat C6 clones were successfully transfected with the antisense-TGFβ construct. Twenty-nine adult female Wistar rats harboring 7-day-old intracranial C6 tumors were then subcutaneously injected with either saline (n = 9), unmodified C6 glioma cells (n =10), or TGF-β-antisense-modified C6 cells (n =70). Animals were followed, for survival, and Fisher!s exact method was used to interpret the significance of differences between experimental groups. The survival of tumor-bearing rats injected with TGF-β-antisense-modified C6 cells was significantly prolonged! relative to the survival of rats receiving injections of saline or unmodified C6 cells alone. Six of the ten (60%) TGF-β-antisense treated animals survived for 72 weeks! whereas none of the nine (0%) animals treated with saline and none of ten (0%) of those treated with C6 cells alone survived past 5 weeks. These results indicate that the genetic inhibition of immunosuppressive cytokines (such as TGF-(3) may reverse the phenotypic immunosuppression caused by such factors, and thereby prolong the survival of C6 tumorbearing animals. Future investigations using cytokine gene modifications in other brain tumor models are warranted. [Neural Res 1998; 20: 742–747]